Surprise Incest

Why didn't he tell them that before they got married?

"How was I supposed to know that we were both related?
Believe me, if I knew she was my cousin we never woulda dated."

— "Weird Al" Yankovic, "A Complicated Song"

The Game the Whole Family Can Play! Haha! Guess what you were doing?

Sometimes in stories, two people meet and just seem destined for romance. Love blossoms in a particular way, or perhaps the two have a loveless Arranged Marriage lying in wait for them instead. But then, someone makes a startling discovery — genetics has struck! The couple-to-be are related — and not in the "same species" sense — and the romance or arranged marriage is called off. The result may be either great rejoicing or great despair. If it's not called off despite the consanguinity issue, intentional Brother–Sister Incest results. Or if the two still want to be together and the author doesn't want to go the incest route, a counter-reveal may show up to prove that the genetics aren't a problem after all.

These days, many people are squicked out by this, so the characters often find out before they tie the knot/do the nasty. This wasn't always the case; Oedipus was very happily (but unknowingly) married to his own mother for many years and had two daughters with her before things fell apart (to the extent that The Reveal resulted in Oedipus' mother killing herself and Oedipus himself stabbing his own eyes out), so this is Older Than Feudalism. Still, this trope is surprisingly common in anime and manga, as well as other Japanese entertainment, due to much more relaxed views on the subject in Japan.

The surprise relationship is usually either brother/sister or half-siblings (sharing one parent rather than both). Parent/child is much rarer these days than it was in ancient Greece, and similarly for uncle/niece or aunt/nephew, thanks to some cultures' taboos on inter-generational relationships, even with no family relations involved.

First cousins, on the other hand, are only borderline squicky since marriage between cousins is actually legal in most places and is quite acceptable in many romance novels. In fact, in the Arabian Nights, a man will call a woman he loves or is married to "daughter of my uncle" because, at that time, marriage between cousins was considered the best option! Because of this, it almost never appears as a plot point since it's a little too close for some folks to be comfortable but not close enough that the plot demands the relationship break up. For relations more distant than first cousins (second cousins, removals and etc.), the squick diminishes with the distance. After all, thanks to how genetics and inheritance works within populations, if you're still having a problem with people who might be, say, 10th cousins or higher, the only relationship you're likely to be assuaged by is one where the couple come from radically different population groups.^note To give a more concrete example: the British panel game QI once made an announcement that they knew for a fact that one of the panelists that evening was a descendent of the legendary 8th century ruler Charlemagne. Who was it? One of the panelists guessed it immediately - all of them. As well as the host, and the audience, and anyone watching at home, assuming they were from Europe at any point in their family tree. And it wasn't that Charlemagne Really Got Around, it was just that with so many generations since his time, everyone, by dint of pure mathematics (again, if you are of a European background) had to have at least some relationship with him.

The relationship is more like to be on the paternal side, because of Mama's Baby, Papa's Maybe. Historically was a fairly common way of making the Veronica of a Betty and Veronica off-limits. This often results in Half-Sibling Angst.

If the characters don't know the truth in advance but the audience does, this overlaps with Dramatic Irony. There's also potential for overlap with Incest-ant Admirer if the admirer isn't aware of the familial relation but the object of their affection is, or if the reveal of said relation bothers one party but not the other.

Expect spoilers.

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Examples:

Anime & Manga

• The prince and princess from Andromeda Stories, a pair of Half-Identical Twins who were Separated at Birth, get into a relationship before learning of their heritage. Weirdly, they decide to stay together after the truth comes out, citing the fact that incest is fairly common in royal families.
• While the characters never know it, Birdy the Mighty Decode sees this: Nataru, the titular Birdy's love interest and childhood friend was, like her, created in lab as a Super-Soldier — the same lab to be precise, which means there's a good chance Nataru and Birdy are brother and sister.
• In the time travel arc of Boruto, Ino teases 12 year old Hinata about how she isn't shy around Boruto. Hinata is Boruto's future mother. Subverted in that Hinata isn't attracted to Boruto.
• Case Closed has a case with Raita Banba and his fiancee, Hatsune Kamon. Uniquely, it turns out that they're identical twins and that the latter has Turner syndrome . Hatsune suspected something was up upon learning that in addition to their identical birth dates, blood types, and unusual ability to know what the other was thinking even when they were silent, that they'd both been adopted after being orphaned as infants in a massive fire that destroyed their birth neighborhood. When she gets the test results confirming it, she... doesn't take it well. And for worse, Raita is accused of having killed her in a Yandere fit. Conan, through Kogoro, has to clear his name.
• In Count Cain, unbeknownst to him, the main character's mother is his father's older sister. He then proceeds to fall in love with his first cousin, which was legal in the time period. The problem is, his cousin is his father's older sister's daughter, making her also his half-sister. There are a couple of other brother/sister couples as throwaway characters, too.
• In Daily Lives of High School Boys, Emi, after days of Cannot Spit It Out, finally finds the chance to confess her love to the visiting Hidenori on a festival, which coincides with his last day in town which happened to be his maternal hometown. But just when she thinks she finally found her chance, Hidenori makes a most surprising revelation to her: they are cousins.
  Emi: "And so, I ended my summer break without being able to do a thing."
• Do You Love Your Mom and Her Two-Hit Multi-Target Attacks?: In the Beach Episode OVA, Masato gets hit on the head and gets amnesia. He becomes attracted to his own mother Mamako. Eventually, he declares his love for her, then grabs her and tries to kiss her. A kraken attacks them and then he suddenly regains his memories.
• Domestic Girlfriend: A Not Blood Siblings example. Natsuo has a crush on his teacher Hina and ends up having sex with Rui, a girl he met at a mixer, in an attempt to forget about her. A week later, his father gets remarried and his new stepmother brings her daughters Hina and Rui to live with them. As his feelings for the girls grow, he keeps trying to keep himself under control by reminding himself that they are his sisters. He eventually starts dating Hina, but that relationship ends because of their teacher/student relationship. Much later, he starts dating Rui, and while their relationship is much more stable, they still have to deal with the fact that they have to hide it from their parents.
• Doraemon: Nobita's father has a brief crush on a mysterious girl he met in the past, not knowing the girl was his own son from the future in Unplanned Crossdressing. Nobita and Doraemon eventually decide not to tell him.
• Dragon Ball Z has a minor example with Bulma gently hitting on Trunks well before she learns that he's her Kid from the Future.
• In the first chapter of Family Compo Masahiko meets Shion and finds her attractive. Later that day he learns she is his cousin. The series sways between them being like siblings and them being Kissing Cousins, with a lean towards the latter.
• Averted in Food Wars!. Asahi Saiba wants to forcibly marry Erina Nakiri to become the greatest chef. He plans to defeat her at the BLUE competition, but is instead defeated by Soma Yukihira. Months later, Asahi and Erina are shocked to discover that they share the same father.
• Subverted in From Up on Poppy Hill. Uma and Shun spend the first third of the movie growing close, until Shun sees a picture of her dad and realizes it's the same man whom he believes to be his biological father. Ultimately, they discover that his father was a friend of Uma's, and that he only took care of him temporarily as a baby.
• Gundam:
  • Depending on your interpretation of their relationship before the big reveal, Kira and Cagalli of Mobile Suit Gundam SEED. They never really got around to doing anything, but they definitely looked like the usual romantic pairing all the way up to the last five episodes of the series. Especially since the first half of Gundam SEED was heavily based on the original Mobile Suit Gundam, with Kira and Cagalli having roles roughly analogous to Amuro and Sayla. Word of God is that this was a deliberate reference to Luke and Leia.
  • Bellri has a crush on Aida throughout the first half of Gundam: Reconguista in G. Fortunately, Aida keeps him at arm's length for various reasons(such as accidentally killing her mentor), so it hasn't gotten anywhere by the time they find out they're siblings, so it's quickly dropped.
• Subverted in I Know All About It. The main character receives a visit from her younger sister, who confesses to being the woman who had sex with the main character the previous night. The main character then says that she knew about her younger sister's feelings for her, and that she went along with it because she reciprocated those feelings.
• In Jewelpet Sunshine, Kanon and Mikage start dating around mid-series; towards the end of the show, Kanon's adoptive-all-along mother reveals to her that she and Mikage are actually twin siblings, who had to be separated because of a misinterpreted prophecy.
• JoJo's Bizarre Adventure:
  • Battle Tendency: A (thankfully) downplayed example happens when Joseph unknowingly peeps on his mother, Lisa Lisa.
  • Stone Ocean: A baby switch eventually led to Perla Pucci dating her older brother Wes Bluemarine, a.k.a. Weather Report. Enrico, upon discovering the relation, tried to keep the damage to a minimum by not telling her and instead hiring a third party to make them break up. Too bad the third party's method of doing this was to lynch Wes.
• Koi Kaze has 27-year-old Koshiro and 15-year-old Nanoka having a chance encounter, going to an amusement park together, forming an emotional connection and spark of mutual attraction, and then finding out they're brother and sister in the first episode. This turns into a deconstruction of Brother–Sister Incest, as the two struggle to resist their mutual attraction while living in the same house but eventually go on to develop a painful and guilt-ridden romantic relationship against their better judgment, fully aware of the devastating implications if their secret got out, but both unwilling to live without the other.
• In one of The Legend of Zelda manga, an adaptation of The Legend of Zelda, Link has a crush on Princess Zelda. Unknown to him, he is her older half-brother who was abandoned because he was half-elf and the previous Zelda didn't want her husband killing him. The manga never shows him learning that they're related. Zelda knows they're related, and doesn't requite Link's feelings, but is never shown telling him that they're related.
• A possible example is Millernium "Milly" Feria Noctum and Kane Blueriver in Lost Universe, although, since they are second-cousins, they're probably distant enough to date if they really wanted to, and the very open ending lends serious doubts as to whether Kane survives the end of the series anyway.
• In Marmalade Boy, Yu and Miki discovers that both their parents have known each other from before their divorce and remarriage, where they are paired together the same way as their current set-up. This causes Yuu to suspect that he and Miki are half-siblings, but their parents reassure them that they are not.
• Maya's Funeral Procession has the main character, Reina, falling in love with a mysterious girl named Maya, only to discover that Reina is the product of her mother's affair with Maya's father and thus they're actually half-siblings.
• Negi and Asuna, one of the most popular and teased pairings in Negima! Magister Negi Magi, are very distantly related by the Lifemaker, maybe closer, but how close was never specified.
• In Neon Genesis Evangelion, Shinji and the second Rei become friends, with a definite undercurrent of romantic attraction. One of several disturbing revelations in the latter half of the series is that Rei is actually a clone of Shinji's dead mom.
• Kanba and Masako subvert this in Penguindrum. They know about their bond and have it more or less clear (though Masako has quite the case of Big Brother Attraction as shown when she kisses Kanba), but it's a surprise to the audience and to Kanba's adoptive sister Himari. Doubles as Twincest.
• Please Twins! played with this one. Each girl came believing that she was the twin sister. They find out about each other and realize that they each have a 50/50 chance of being the twin. They both fall in love with the man a few episodes after this. The irony being the anime had one of the girls be the guy's sister, and the novelization had the other one.
• In Saiyuki, fraternal twins Cho Gonou and Cho Kanan were separated at a very young age when their parents divorced, one parent taking each child. Years later, they met at school, fell in love, discovered their relationship to one another, and became lovers, in that order.
• Sailor Moon:
  • Shingo Tsukino has a huge crush on Sailor Moon, as he's unaware that she is actually his sister Usagi, whom he has a far more adversarial relationship with.
  • Chibiusa is Usagi and Mamoru's Kid from the Future. As soon as she arrives in the present, she gets an Accidental Kiss with Mamoru. She is attracted to her own father and competes with Usagi for his affections. The surprise is on Usagi and Mamoru's side when they eventually find out who she really is.
• Averted in Slayers: Thankfully, Zelgadis stating that Rezo was both his grandfather and great-grandfather turned out to be a translation error.'
• Falan and Ilsaid's dad in Vampire Game did not inform them that they were related, until his son asked for his sister's hand, that is. He then only told his Unfavorite, though.
• Vampire Knight: When Kaname turns Yuuki into a vampire, restoring her memory, she reveals to the audience that Kaname is her brother. Ah, so the Love Triangle will be easily solved, won't it? Wrong. Kaname confirms she's his sister and states she was born to become his wife. Then he asks the other why they look surprised — this is very common among pureblood vampires, and in fact, their own parents (Juri and Haruka) were siblings and Happily Married. Later it turns out that Kaname wasn't her brother, but a distant ancestor who had been asleep for hundreds, if not thousands, of years and her real brother was given to him as a blood sacrifice so that he could be revived. It's still incest so it's double subverted. The situation is exactly as complicated as it sounds.

Comic Books

• Age of Bronze: One of the chieftains mentions he unknowingly married his mother, but fortunately a snake showed up in the marriage chamber in time to prevent it from happening (and then they learn they're related, so they attribute the serpent's presence to his father Herakles intervening).
• Blacksad: Hans Karup unknowingly married one of his own daughters after she came of age. She was actually aware of their family relationship, and wouldn't let him touch her. The marriage was in fact all part of a decades-long revenge plot to hurt him for previously leaving their mother to her death.
• ElfQuest:
  • It may never have been revealed to the characters, but Cutter once got it on with Kahvi during a pre-battle orgy, and Kahvi takes up with him while Cutter's family is lost in time, though it doesn't really work out. Much later, readers learned that Kahvi is the daughter of former Wolfriders chief Two-Spear. Cutter is a direct descendant of Two-Spear's half-sister, Huntress Skyfire, making Kahvi his cousin four times removed — which, especially considering the small gene pool of the Wolfriders, isn't spectacularly close. Also, with Recognition preventing conception for any but good genetic combinations, the elves may not have an incest taboo.
  • Also, if one looks at Scouter/Tyleet's relationship, you'll realize they're second cousins (Brothers Longbranch and One-Eye, Longbranch sires Nightfall, One-Eye sires Scouter, Nightfall has Tyleet, Scouter and Tyleet Recognize). It makes sense, however, that such in-pairings will happen in such a small tribe — so yes, Recognition probably does take care of the biggest problem with incest. Thankfully, however, we haven't been subjected to any closer pairings...
• Jack from Fables doesn't find out that he's adopted and that the Page sisters are also his half-sisters until after he's already slept with each of them. He takes the news relatively well, his sisters, not so much.
• A story arc in The Fabulous Furry Freak Brothers has Fat Freddy looking for his old home in Cleveland, broke, hungry, and bemoaning his perpetual bad luck. Just then, to his delight, a cute girl appears, befriends him, takes him home, feeds him, and joins him in the bathtub. A car pulls in and she warns "Here come my parents!" — Freddy sees them and exclaims "Holy Toledo, these are my parents too!"
• Jimmys Bastards: Jimmy Regent (a James Bond parody) turns out to have spawned an entire army of, well, bastard children over the years with every Girl of the Week, many of which have united for revenge against him for not being helping raise them. The villain's plans hinges on getting Jimmy to sleep (unknowingly) with his daughters and reveal this at the opportune moment to break him. It works.
• MAD occasionally uses this.
  • In a list of cliché movie props, one Arab beggar reunites his necklace with that of the Caliph's daughter, whom he loves, and in doing so, learns that they are brother and sister. The love affair ends before it starts.
  • In the parody of Maverick, the final line:
    There's still one final plot twist — you can't marry your own sister!
• The Mighty Thor: In an issue of Jason Aaron's run, a young version of Thor is pulled out of the distant past and enslaved on a world full of Gods who have been kidnapped from various eras of history. He meets three beautiful young goddesses, sisters. While two of them are unimpressed by him, one, Ellisiv, is enjoying the sight of a young Thor in a loincloth. They turn out to be his descendants from the far future.
  Ellisiv: Thor? Oh my Heavens... I've been having impure thoughts about my grandfather.
• Shazam!: The Monster Society of Evil has a thankfully low-key example: Mary seems to have a Precocious Crush on the superhero who just saved her from being eaten by alligator-men and kisses him on the cheek, only to find out a few pages later that he's actually the Older Alter Ego of her long-lost big brother. She thinks it's gross, but he's so happy to have tracked her down that he's just amused by the whole thing.
• Supergirl: In Many Happy Returns, Kara Zor-El and Kon-El meet and find each other cute (Kara is visibly smitten with him). Neither of them is aware that Kara is a cousin of Kon's genetic template.
• Superman:
  • Superboy (1949): In issue #217, Superboy finds a new and gorgeous Legionnaire, becoming instantly entranced with her. He backs off when he learns her new teammate -Laurel Kent- is her 30th century descendant, who explains he felt smitten with her because she looks right like his (to him future) wife.
  • Superman: Red Son. Although nothing ever comes of it, Superman and Lois Lane are clearly in love. It's revealed at the end of the comic that Superman is not an alien but a highly evolved human from the far future sent back in time as a baby, and he is a distant descendant of Lois and her husband Lex Luthor. That being said, the family connection is so many generations removed that they're probably no more genetically related than any two random people.
• In the EC Comics Weird Science story "The Last Man" (#12, 1952), a man returns to Earth after a long space journey only to find it removed of any humans. After a long search, he finally finds a woman, but before they can make plans to repopulate humanity, they shockingly discover that they are brother and sister.
• X-Man: After he arrives in the 616 reality, Nate Grey is found by a redheaded young woman called Maddie, who's lost most of her memory. She turns out to be Maddie Pryor, clone of Jean Grey, who Nate accidentally resurrected when subconsciously reaching out for the 616 version of Jean. Why would Nate have reached out to Jean? Why, she's his genetic mother — and thus, so is Maddie. The resemblance didn't matter — he'd only met his reality's version of Jean once, and had sensed a connection, even if he didn't know what it was. Anyhow, Nate and Maddie get along remarkably well, building a connection and a developing sense of Unresolved Sexual Tension, which the narrative (and some fans) gleefully fanned the flames of. Then Nate found out about his connection to Jean and Maddie — thankfully before they'd got closer than an Almost Kiss or two. He backed off sharply. Maddie, on the other hand, was a textbook Tsundere (to occasionally murderous extents) whose attitude was neatly summed up by the notoriously suggestive cover to issue 41.

Fan Works

• In Apollo Justice: Ace Attorney, we see the protagonist, Apollo Justice. His attractive assistant is Trucy Wright, Phoenix Wright's daughter. They got a bunch of Ship Tease in-game until it was revealed that Trucy was adopted, and she's Apollo's half-sister through their mother Thalassa. Oddly, it still hasn't stopped the fan pairing from still occurring. This is probably because while the players learn that Trucy and Apollo are related, they themselves never do (although at the end of Phoenix Wright: Ace Attorney – Spirit of Justice, Phoenix and Thalassa decide it's time for them to know).
• In The Darkness Series, a Voldemort/Harry fic, Harry learns he's related to Voldemort on both sides of the family tree. They don't think too hard about it.
• Dragon Ball Z Abridged:
  • A half-example happens, that is possibly an Homage to Back to the Future. Trunks travels back in time but keeps quiet about being a time-traveler so he doesn't change the past. Then his future mother Bulma starts hitting on him:
    Bulma: So hey, like just gonna throw this out there: you're really cute.
    Trunks: Well, you know, my mom always said I was a cute kid...
    Bulma: Oh a momma's boy huh? I'll be your mommy. (wink)
    (Trunks forces a smile while screaming in his head)
  • Upon finding out the truth a few years later:
    Bulma: Oh my god, I solicited my son for sex.
  • What makes this hilarious though, is that once Trunks returns to the future to report on his progress, Future Bulma is rather nonplussed at the idea that her past self hit on him:
    Trunks: Before you found out I was your son, in the past, you... might have made a pass at me.
    Bulma: Well duh.
    Trunks: MOM!
    Bulma: Hey, it's not my fault your dad's genetics and mine got along like chocolate and peanut butter.
    Trunks: Is... that why you used to call me your "little peanut butter cup?!"
• Played straight in the Avatar: The Last Airbender fanfic Embers (Vathara) where it is revealed that the relationship between Zuko and Mai was a secret case of Kissing Cousins orchestrated by Azula in order to have leverage on them.
• The How to Train Your Dragon fic "Berserkers & Hooligans" reveals that Heather has secretly been essentially Hiccup and Astrid's on-off mistress for years, to the extent that only the three of them know that Hiccup is the father of Heather's son Oswald. During one visit after the dragons leave, Hiccup and Astrid's daughter Zephyr is dared to kiss Oswald, and the three parents are momentarily concerned before Zephyr makes it clear that she found the kiss disgusting and compared it to kissing her brother without even knowing that Oswald is her brother, assuring the parents that they have no concerns on that front (although they still make plans to at least tell their children the truth about Oswald's parentage).
• Technically at least referenced in An Extraordinary Journey; when the SGC, the remaining Cylons and the survivors of the Twelve Colonies find a survivor on the Earth of the Thirteenth Tribe, she is swiftly identified as the source of the DNA used to create the Number Six Cylon, who reveals that the Number Twos are based on her father. As a result, technically any Twos and Sixes who have gotten involved are committing incest, with the Two present when she reveals their connection quickly expressing discomfort at this revelation.
• Fates Collide: Mercury Black is attracted to Ushiwakamaru, but is unaware she is his long lost sister. She knows of their relationship, but doesn't have the heart to tell him and is apparently unaware of his attraction. When he eventually finds out, he is shocked, but then becomes happy he has a family member who cares about him and they have a normal sibling relationship.
• The dōjinshi Golden Sun Gag Battle! featured a 4koma in which Ivan's first use of Reveal was to spy on Hama through her clothes. Gag Battle was based on the first game and published prior to the release of the second, which revealed that Hama was Ivan's sister, making this a meta example. Mia and Alex, another popular pairing due to their shared history, were revealed to be cousins in Dark Dawn.
  • While not strictly an example since they and the fans know darn well they're related, the fandom's unofficial name for the Felix×Jenna pairing is "Oopsie-shipping".
• In Hard Reset, Twilight figures she might as well use a "Groundhog Day" Loop to have a one-night-stand with Princess Luna. In the sequel, she finds out she had, long ago, another suitor. One that Twilight's also attached to in a way. Celestia then reminds Twilight that 1,600 years is probably sufficient time. 'You’re probably more closely related to a random unicorn wandering the streets of Canterlot, genetically speaking.'
• Higher Learning: While Shinji was stuck into the Twelfth Angel Asuka turned to Kaoru to have a shoulder to cry on. After he spent a while reassuring her, she felt something familiar on him and kissed him on impulse. Right away she felt guilty, got scared and ran away. At the next morning, Kaoru apologized and said he would resign if she wanted, but she said not and apologized in turn. They never brought it up again, not even when Kaoru confessed that he was her GRANDSON.
• Narrowly avoided in How to Break a Family. Arthur is convinced to see a prostitute but is turned off when it turns out she's only fourteen. He finds out a moment later that she's his sister Kate. The two were separated when their parents divorced fourteen years prior.
• Due to the growing relationship between Asuka, Rei and Shinji in Neon Metathesis Evangelion, Rei and Shinji are headed that way.
• In Love Kills, a Percy Jackson and the Olympians fanfiction, the main character, Jade, falls in love with Luke only to find out that he's her brother. You'd think his name would have been a giveaway.
• Momentary Weakness: Downplayed. Sena invites Nia back to her bedroll, unaware that Nia is her Honorary Aunt (she doesn't even know what an aunt is, as she's only been recently been introduced to the idea of families). Nia politely declines, noting that she's Happily Married... and then, when Sena isn't paying attention, mutters that Sena's mothers would murder her if she took advantage.
• A brief example of this features in the Charmed (1998) fanfic Once And Future Witches, when circumstances prompt the Charmed Ones of 2007 to go back in time six years accompanied by Chris (who has come back from the future when Wyatt was attacked by a curse). Once they have assured the Charmed Ones of 1999 that they’re real, the young Phoebe asks if Chris is “[her] own hunk of Whitelighter”, leaving her older self embarrassed and young Phoebe herself disgusted once older Piper clarifies that Chris is her future son, and hence Phoebe’s nephew.
• In the Frozen fanfic The Queen of Hearts, Hans was a Child by Rape conceived during a war. He was raised in the Southern Isles, not Arendelle alongside his half-sisters Elsa and Anna (both of which he tried to marry). His parents tried to avoid this by never having the half-siblings meet, but Hans found his way to Arendelle anyway.
• Played for tragedy in the Star Wars fanfic The Shadows Suit Me between Luke and Leia.
• Somos Familia: Downplayed. Ignacio tries to woo Coco, whose father turns out to be his half-brother. However, Coco only returns his interest as a knee-jerk reaction after getting into a fight with Julio. She dislikes Ignacio and quickly dumps him before their relationship gets physical. Additionally, the only character to learn about their relationship so far is Hector, who is too busy processing his father's identity to reflect on Ignacio pursuing Coco.
• The Frozen fanfic Stolen Ice has this occurring to Elsa and Anna. They were separated at a young age but come across each other as adults and fall in love. They don't learn they're sisters until late into the story.
• Sword Art Online Abridged gets into this despite changing Kazuto and Suguha's relationship from an unrequited Big Brother Attraction/Kissing Cousins deal to something much more antagonistic. After bumping into each other one evening in Alfheim Online, Leafa is able to figure out that the Spriggan she's been adventuring with is her brother Kazuto after he properly introduces himself as Kirito. She logs out to have a Cluster F-Bomb-ladden rant because she was just caught roleplaying by someone she constantly mocks, then remembers an even more embarrassing detail:
  Suguha: Oh Jesus fuck, I said my brother had a sweet patootie! [shrieks and begins sobbing into her pillow] Noooo, nooooo, NOOOOOO!!
• In the RWBY fic Unexpected Sisters, Yang and Ruby are co-workers who find out that they're half-sisters. In hindsight, it makes the time Ruby asked Yang out (and she declined) even more awkward.
• White Sheep (RWBY):
  • Subverted. Due to some coincidences and assumptions, Qrow believes that Jaune is his sister Raven's son, and therefore his niece Yang's half-brother. Since they're kind of dating at this point, Qrow is horrified, and tries to sabotage their burgeoning relationship. This actually leads to their relationship getting stronger. Thankfully, Qrow was wrong, and Jaune is not related to Yang at all.
  • And then there's the moment where Qrow discovers the girl he is in the middle of having sex with is Jaune's sister—while he still believes Jaune is Raven's son. There is a lot of screaming.
• Good News and Bad News (an M-rated MLP fic): Twilight's been dating Flash Sentry, and when she discovers she's pregnant, they go to tell Twilight's father... but before they can say anything about it to him, he happily greets Flash as "my boy" and, at Twilight's confused reaction, admits that Flash is his son from his first marriage. The couple are stunned when they realize what this means for them.
• One-sided example in Yin-Yang. Adam flirts with Adora when they first meet, but she isn't interested in him at all. After they learn that they are siblings, Adam is really glad Adora rejected him.
  Adam: I... I'm not sure how I feel about this. Other than that I've never been so happy to be rejected by a girl in all my life.
  Adora: Yeah... lucky us.
• In Going Another Way, after being Rei's girlfriend for several months, Shinji learns that, because Yui Ikari's DNA was used to create Rei, they're technically siblings. However, due to the countless other women who's DNA was also used to create Rei, the amount of Yui's DNA that actually makes up Rei is less than 1%.
• Played with in Sibling Revelry, in that the Empire at large is under the impression Luke and Leia are in a romantic relationship, so when Vader learns early they're siblings he tries repeatedly to have this sprung on them before she gets pregnant. Too bad that by the time they find out they're trolling a "Fred Antilles" (Vader's spy on the Home One) by pretending they're romantically attached because he's opposed and finding out only makes them pretend they're happy.
• In Lacrime D'oro del Vento Aureo, Giorno has a brief crush on the visiting Josuke. Unbeknownst to Giorno, the two are actually relatives and part of the Joestar family^note For clarification, Giorno is the illegitimate son of Jonathan Joestar after Dio stole his body, while Josuke is Jonathan's great-grandson.
• In this Fate/Grand Order fancomic, it's heavily implied that this is the reason Lancelot feels ill after finding out that his adoptive mother Nimue was a split personality of Morgan. The reason is that Lancelot harbored feelings for his king Artoria (enough that he conspired with Gawain to convince her Lancer self into wearing a bunny suit), and is horrified to learn that she's actually his adoptive aunt.
• Invoked in Stone Streak, where to get Chloe to stop making him her boyfriend, Adrien points out that once Luka and Chloe's older sister Zoe get married, that would make Chloe and Adrien aunt and nephew^note In the story, Adrien was adopted by Juleka and Marinette, which also make Luka his uncle and Zoe his soon-to-be aunt.
• The Final Confession: During Emilie's Video Will, she reveals that as a Puella Magi she was unable to have children as she was a soul gem operating a corpse. Instead, her son Adrien was originally one of Audrey Bourgeois's twins^note Though Emilie doesn't consider Audrey worthy as a mother given she was quick to report as only giving birth to a daughter rather twins. After watching, Chloe, horrified that the boy she had a crush on was her twin brother, vomits in a nearby trash can.

Films — Animation

• In-Universe in Encanto: Bruno creates elaborate telenova storylines for his pets to act out, one of which involves an amnesiac woman unknowingly in love with her nephew.
• Kind of inverted in Meet the Robinsons. Lewis goes to the future, spends time with the Robinson family, and begins to see Franny as a bit of a mother figure (even actually calling her mom and almost being adopted by her at one point) before finding out that she is actually his future wife. One wonders how he wasn't the least bit squicked out when he meets her for the "first time" in the past.

Films — Live-Action

• 17 Again (2009): Maggie is attracted to and tries to seduce "Mark"... who is her father, Mike, aged down. Mike understandably rejects her advances. She never learns about the fact, though.
• ABCs of Death 2: At the end of "Z is for Zygote", the husband is about to take his 'wife' to bed to make another baby after she tells him that she has lost the child she was carrying. If you believe that the child has taken over her mother's body and is wearing her skin (and this is not just a delusion of the mother), then this would be a case of incest.
• In Angel Heart, Harold Angel is investigating the disappearance of Johnny Favorite. In the process, he has sex with Johnny's biracial daughter Epiphany Proudfoot. It turns out that he himself is Johnny later on. To make matters worse, he later killed her while under Satan's influence.
• Inverted in Ator the Fighting Eagle: Ator and his sister Sunya are "in love" and want to marry, only later to find out that Ator was adopted, meaning they aren't siblings at all and can now safely marry.
• Factors into The Reveal in August: Osage County, but not the way the characters expect. Growing up, protagonist Barbara and her sisters had just one cousin on their mother's side, known in the family as Little Charles. Middle sister Ivy eventually admits to her sisters that she and Little Charles have fallen in love, as a result of him helping her through a bout with cervical cancer that no one else in the family knew she had. Barbara finds this awkward, but not horrifying, especially since Ivy's unable to have children as a result of her cancer surgery. Then their aunt (their mother's sister) reveals to Barbara that Little Charles is actually their half-brother, the result of her having an affair several years ago with Barbara's father.
• In the film An Awfully Big Adventure, P. L. O'Hara, an aging actor, seduces a teenage girl, only to find out later that she's his daughter. The distraction caused by this discovery leads to his death.
• Parodied in Back to the Future where Marty knows that young Lorraine will be his mother, but she doesn't, so she pursues him romantically to his great dismay. The attraction conveniently disappears after she kisses him, saying that it was like kissing her brother. Chalk it up to women's intuition, the timeline trying to correct itself, or just finally cottoning on to Marty's obvious discomfort.
• The major couple in The Beastmaster turn out to be cousins, though not one person ever remarks on this. Considering that she's described as his half-brother's cousin, maybe they're not blood cousins after all. She could always be the niece of the king's second wife.
• The Japanese film Bubble He No Go has a father sending his daughter (who doesn't know he's her father) back in time some 20 years to find her mother, only to find her younger father instead, who tries to shag her, but she refuses, only to almost give in but then he shortly before realizes that... and so on.
• Code 46 deals with a future where, due to extensive cloning, there is a likelihood of a close genetic relationship between perfect strangers. Maria becomes pregnant by William, only to discover that, biologically, she's his mother; due to the laws, the baby is aborted and Maria's memories are modified to forget she ever met William, but unfortunately, nobody told William. He finds her again, only this time their intimacy triggers an implanted suggestion, causing Maria to turn herself and William in, this time resulting in a memory wipe for him and for her exile with her memories intact.
• In Curse of the Golden Flower, Chan and Wan eventually find out they're half-siblings, and take it about as well as you'd expect.
• Played for Laughs in Dirty Work: the two best-friend protagonists find out they are actually half-brothers. One of them becomes upset with the revelation, and the other cheers him up by reminiscing about their childhood, pointing out they practically grew up like brothers anyway. At first, it goes fine, until...
  Mitch: Hey, hey! Hey, you remember in 5th grade when I was under the monkey bars and I sneaked a peek at your sister's underwear? Remember that? Hey, no no! I was sneaking a peek at my own sister's underwear!
  Sam: That's right! Yeah, and then remember in the 12th grade, you had sex with her?
  Mitch: [short awkward silence as the Fridge Horror hits them both] Okay, enough reminiscing.
• Funeral Parade of Roses: Gondo gets a very unpleasant surprise when he gets a look at Eddie's photo and recognizes the man with the burnt-out face, Eddie's father...it's him. (It's a Gender Flip update of Oedipus the King.)
• Becomes a main plot arc in Incendies when the twins discover when their mother sent them to find a lost brother and their lost father, that the person is in fact the same!!!
• In Japanese film Inugami, Miki and Akira discover that they are mother and son. They also discover that Akira is a product of another, similarly themed trope.
• In the film Jean de Florette, Le Papet (Yves Montand) and his nephew Ugolin (Daniel Auteuil) drive a hunchback, Jean (Gérard Depardieu), to his death in order to get his land. In the sequel Manon of the Spring, Ugolin sees the hunchback's daughter Manon (Emmanuelle Béart) bathing in a pond and falls desperately in love with her. He commits suicide when she rejects him. At the end, his uncle Papet learns that Manon's father was his long-lost son. That means Ugolin was in love with his own cousin.
• Parodied in Joe Dirt — in Joe's quest for his lost family, he finds and goes out with an attractive girl who he realizes afterwards was his sister, goes back to tell her and explain why he can't date her (and probably ask her for information), but somehow gets seduced into sleeping with her, then tells her his suspicion. She then explains why she couldn't possibly be his sister, and that they can make love again. Joe puts on a mischievous face and the camera cuts back to the outside of the house... as nothing happens.
  Jill: Would it help if you went back to thinking I'm your sister?
  Joe: What?! Like I'm some sort of white-trash perv?!
  [cut to the outside of the house, the foundations shaking and a nailed-up hubcap clattering off to orgasmic cries]
  Jill: I'm your sister! I'M YOUR SISTER!
  Joe: AAAAAAAAAHHHH YER MY SISTER!
  • Joe then assures the radio people he's telling the story to "No, that last part didn't really happen, I just thought it'd be funny."
• In The Judge, Hank seduces a girl in a bar. Then finds out she is the daughter of an old flame. And the math makes it possible to be Hank's as well! It turns out she's his niece, as the disgruntled ex slept with Hank's brother.
• Kaboom!: In the climax of the film, it is revealed that Smith and London are half-siblings, both having the same father. This is a nasty surprise for them, since they've been boning regularly through the movie.
• In the original cut of Kate & Leopold, Kate's ex-boyfriend is Leopold's great-great-grandson. Due to Stable Time Loop, this means Kate's ex, who she spent years with, is also her great-great-grandson, something that hadn't occurred to the director. This is excised from the theatrical version, but remains in the director's cut.
• In Lone Star (1996) two characters that had dated in high school over their parents' STRONG objections reconnect as adults. At the time, they had assumed their parents objected out of racism as he is white and she is Hispanic (with the story taking place in the south). They later find a photograph of his dad and her mom and realize why their parents were so opposed to them dating, namely, that they're half-siblings with the sister being born out of an affair. But they're very much in love and she says that, due to complications in her last pregnancy, she can no longer have children. It's implied that they will stay together.
• My Chauffeur flirted with this. As one of several seeming reveals about who the female lead's "real father" was. Apparently, Mom got around.
• Invoked in Nutty Professor II: The Klumps when Grandma Klump tries to seduce Buddy Love when mistaking him for the stripper for a bachelorette party, unaware that Buddy is essentially a genetically-altered clone of her grandson.
• Oldboy, in which the main character is the victim of an elaborate revenge/imprisonment plot, the final result of which leads him to discover that the woman he has fallen madly in love with is, in fact, his daughter. He, uh, doesn't take it so well.
• In the drama film Powder Blue, a stripper (Jessica Biel) whose young son is in a coma, performs a lapdance for a middle aged male customer (Ray Liotta) there to see her. Unbeknownst to her, the man she's giving a lapdance to is actually her long-lost father and the man, appropriately repulsed, moves her hands and body away from him as he just wants "a hug, not a tug".
• In Red Riding Hood, Lucie was in love with Henry, but doesn't realize that they share a biological father. Fortunately, nothing actually happens between them. Unfortunately, it factors into a couple deaths.
• In the Michael J. Fox film, The Secret of My Success, Brantley is asked to escort the wife of his boss to her country home. She takes an immediate liking to him and convinces him to stay for a swim, which leads to her seducing him. Not long after, Brantley realizes that she is his Aunt Vera (by marriage, as his boss is his blood-related uncle, Mr. Prescott). Brantley is disgusted, but Vera isn't - she later pursues him sexually.
• In Soapdish, Jeffery starts dating his ex-girlfriend Celeste's young protege Lori. Celeste strongly objects to this, but they shrug it off as jealousy. Celeste is finally forced to admit that Lori is their daughter. Celeste and Jeffery separated a long time ago and she did not inform him that she was pregnant. While raising Lori, she told her she was adopted. Jeffery and Lori are horrified but glad they were stopped before they could kiss.
• In the American college comedy Sorority Boys a character, Jimmy becomes infatuated with his former frat brother and actual biological older brother Adam while the latter is Disguised in Drag for plot reasons. Adam, naturally, tries desperately to fend off his unwitting brother's advances without blowing his cover. This is played for laughs over the course of the movie until a scene where it is heavily implied Jimmy raped Adam while "she" was passed out in his room. Needless to say, after The Reveal, things become very awkward between them.
• Enforced in Star Wars due to a series of script rewrites and retcons. A New Hope suggests Luke Skywalker has a crush on Princess Leia Organa,^note Alan Dean Foster's novelization and the first comic book adaptation, Star Wars (Marvel 1977), and Splinter of the Mind's Eye make it explicit and mutual and it and The Empire Strikes Back have a minor Love Triangle between them and Han Solo: at one point, Leia kisses Luke on the mouth, but the movie makes it reasonably clear she did it just to spite Han. After Empire, however, George Lucas decided to cancel the then-planned sequel trilogy and condense its major storylines into a single film, which became Return of the Jedi: the "other last hope" that Yoda and Obi-Wan refer to in Empire was originally just meant to remove Luke's Plot Armor as the main character, but became Luke's sister from whom he had been Separated at Birth,^note an idea originating in early versions of The Star Wars, which became A New Hope and Leia was the only established character his sister could somewhat-plausibly be. In subsequent Expanded Universe media, the siblings invariably say they try not to think about it on the rare occasions it's brought up.
• That Night in Varennes: Restif the pornographer, in one of his dirty books, tells a story of having sex with a High-Class Call Girl and only finding out afterwards that she was his daughter. Of course, since the movie shows he's actively engaged in an incestuous relationship with a different daughter, he probably wasn't bothered.
• Three Seats for the 26th, a French movie where Yves Montand plays himself and buxom sex bomb Mathilda May plays his illegitimate daughter Marion (a character created for the movie, not based on any real person). They meet and immediately feel attracted to each other and eventually sleep together. At some point, Marion's mother tells her that Montand is her biological father, Marion reacts... with a cute "oopsie!" face and isn't bothered at all by The Reveal. Montand, however, is pretty horrified but after seeing Marion's nonchalant attitude towards the whole mess, he relaxes and realizes that perhaps Parental Incest isn't such a horrid taboo, all things considered. They all become a happy family.
• In Tromeo and Juliet, the eponymous pair find out at the end they're brother and sister, but decide to get married anyway. In true Troma fashion, they have hideously deformed kids.
• In War, Inc., Yonica keeps hitting on Hauser, which creeps him out because she's a teen and he's an adult. At the end, they find out they're father and daughter.
• In the extended cut of Wild Things, Suzie is revealed to be Kelly Van Ryan's aunt (whose grandfather was a notorious philanderer). As part of Suzie's scheme to con her older half-sister Sandra Van Ryan (Kelly's mom) out of millions of dollars, she knowingly had sex with her own niece several times. Although no one except Suzie was ever aware of this and Kelly never learns the truth.
• The 1920 silent film Within Our Gates has a flashback to the protagonist almost being raped by a white man. He then notices that she has the same distinctive birthmark on her chest that his daughter with his ex-wife did. Sylvia herself has quite a complex about the fact she's half-white.

• In Zathura, Lisa immediately starts harboring a crush on the astronaut once she awakens after having been being frozen for most of the movie. He tries to brush off her advances, presumably because she's underage. Later in the film it's revealed that the Astronaut is actually her little brother Walter from an alternate future. She's... less than pleased. (Since it's a space-themed sci-fi film, this could debatably be considered a loose Star Wars reference.)

Jokes

• Subverted in a joke where a young man tells his father he's going to ask out the girl next door. His father looks grave and says "You can't. I've never told anyone this, but you need to know ... many years ago I had an affair with her mother, and, well..." Horrified, the young man runs out of the room where his mother asks what the problem is. He explains "I'm in love with the girl next door, but Dad says he's her father!" And his mother replies, "Don't worry about that. He might be her father, but he's not yours!"

Literature

• One of the three protagonists in the web serial Addergoole Shahin has an intense romantic affair with another student Emrys. Later, it turns out that they're half-siblings, sharing a father. This doesn't seem to deter them in the least, as they wind up committing and getting married.
  • As a bonus, the couple above is involved in a sort of love triangle with a third person who, unbeknownst to all three at the time, is actually their father.
• Pops up in V. C. Andrews's work (original and ghostwritten).
  • In Garden of Shadows, Corrine and Chris, who in prior books were already half-uncle and niece, turn out to be half-brother and half-sister as well (though they seem to be unaware of that part).
  • In the second book of the Casteel Series, Dark Angel, Heaven meets Troy, her late mother Leigh's step-uncle. They fall in love, have sex, and get engaged when Tony, Troy's brother and Leigh's stepfather, reveals to Heaven that she was the product of Tony's rape of Leigh, making her and Troy niece and uncle by blood.
  • The Cutler Series has Dawn going out with Philip Cutler, only to learn that she's his long-missing sister. Dawn wants to leave the relationship behind, but Philip doesn't take it well.
  • At the start of the Landry Series, Ruby is dating Paul but quickly ends their relationship when her grandmother reveals to her that Paul is her half-brother. Paul takes it better than the above-mentioned Philip, but he never truly gets over Ruby.
• Severian of The Book of the New Sun never knew who his family was, so this was always possible given the number of women he took to bed. At the end of Citadel he discovers that Dorcas is actually his grandmother, who had been drowned decades ago and then returned to life by the Claw. He notes that he still loves her, but she loves the past more than him.
• Boone's Lick: Downplayed. Shay thinks the local prostitute is pretty, but never tries to sleep with her either before or after learning she's his mother's half-sister.
• In A Brother's Price, Jerin and Ren hit it off to the point where he's left a Technical Virgin. Then they find out that because his grandmothers kidnapped a prince, they share great-great-grandmothers, making them first cousins twice removed, second cousins once removed, or third cousins. Jerin is initially disturbed by this revelation, but Ren says it's fine and later others agree. Many of the nobility are somewhat more inbred than commoners and actually, this reveal makes him a Suddenly Suitable Suitor.
• In the first trilogy of The Chronicles of Thomas Covenant Thomas is the object of open sexual advances by High Lord Elena, who he eventually realises is biologically his daughter, though (thanks to the time discrepancy between the Land and 'our' world) she actually appears to be older than him. Unsettlingly, she knew all along. Though this discovery explains why he finds her emotionally compelling, he continues to wrestle with having some degree of physical attraction to her - made all the more complicated by the fact that he believes his entire experience is a delusion.
• In Linda Castillo's The Dead Will Tell William "Hoch" Yoder's wife Hannah is actually Ruth, who was born after his mother Wanetta was abducted, raped, and left for dead following a botched home invasion that resulted in the deaths of her husband and all of her children save William. Ruth maintains her father is Wanetta's murdered husband, but it's more likely it was one of the rapists. Either way, after Wanetta died, Ruth created a false identity and married William, knowing full well what they were to each other, for the purposes of Gaslighting him since he had unintentionally caused the deaths of his siblings by leaving them with a lantern that overturned and sparked a fire and Wanetta held him responsible, which is also why she never let him know she was still alive even after regaining her memories. It's vaguely implied that Ruth causes William to take his own life by revealing their true relationship at a particularly vulnerable moment for him once he learns his mother actually survived for many more years but wanted nothing to do with him.
• In the Jin Yong novel Demi-Gods and Semi-Devils, all the women Prince Duan Yu has relationships with turned out to be one of his father's natural daughters. Subverted in that Duan Yu was later revealed to be the product of a one-night-stand between his mother and a rival to his father's throne.
• The Kwisatz Haderach breeding program of the Bene Gesserit in the Dune series does rather a lot of this if the crosses mentioned in the books are a representative sample. The people involved are generally unaware, at least at the time.
  • According to their plan, Jessica was supposed to have a daughter with Duke Leto Atreides. The daughter was then supposed to be married off to a Harkonnen heir in order to end their millennia-long rivalry. However, Jessica is actually Baron Vladimir Harkonnen's daughter (although she didn't know until Paul told her). This means that the plan was for Jessica's daughter to marry her cousin.
• Subverted in The Elvenbane by Andre Norton and Mercedes Lackey when Valyn is determined to push away Shana even though he admits that she is lovely and knows that she has a massive crush on him. He does this because he suspects that she is his half-sister. He actually goes so far as to set her up with his sidekick in a "handfasting" ritual. However, he picks up the Idiot Ball when he refuses to tell her why he is rejecting her even though she is hurt and angry about it. His excuse? She was Raised by Wolves (or dragons, in her case) and he's not sure if such things matter to her, in spite of the fact that she has already shown herself to be intelligent and fairly well-versed in human and elven culture.
• Cthulhu Armageddon volume The Tree of Azathoth has Booth discovers that Martha Booth was his biological sister, of sorts, due to the fact that both of them are the children of Alan Ward. This was notably foreshadowed by the fact that Martha and Alan as well as Gabriel (Martha and Booth's son) share the trait of albinism.
• In Frances Burney's 1778 novel Evelina, the eponymous heroine saves one Mr. MacCartney from suicide, since he believes he fell in love with his sister. MacCartney grows to idolize his savior Evelina in a quasi-romantic fashion. However, at the end of the novel, Evelina is revealed to be his real sister, while his original beloved was an unwitting (and unrelated) impostor.
• A rare ray of sunshine in The First Law is the romance between Savine dan Glokta and Crown Prince Orso dan Luthar. She's an ambitious social climber, he's a feckless royal layabout. After Savine has a close call in the uprising that forms the centerpiece of A Little Hatred, Orso proposes marriage, and Savine agrees. She comes home and glowingly tells her mother that she's going to be queen...and her mother is nearly sick. It turns out the man she knew as her father isn't her biological father; her mother was knocked up by the king, and they were married in order to keep her safe. Meaning that Savine and Orso have the same father. She immediately breaks it off with Orso and doesn't tell him why until after a bit of civil war in the next book.
• At the end of the Marquis de Sade's story "Florville and Courval" (from his collection The Crimes of Love) the heroine discovers that she has unknowingly had a child by her brother, killed that child in self-defense when he was trying to take her sexually, and married her father.
• In Robert A. Heinlein's Friday, the eponymous Friday has a bit of a crush on her father-figure employer, who is later revealed to actually be her father... or at least a male who contributed some of her DNA, Friday's genealogy being somewhat non-traditional.
• In The Good Daughters by Joyce Maynard, Ruth and Dana are born to different families in the same hospital on the same day, and growing up are referred to as "birthday sisters" by their families. As an adult, Ruth dates Dana's brother, Ray, until her parents step in and say something to Ray and he breaks off the relationship. Ruth doesn't learn until much later that she and Dana were switched at birth, making Ray her biological brother, and he had broken up with her because her parents told him this.
• Grandmaster of Demonic Cultivation: Mo Dao Zu Shi: Jin Guangyao and Qin Su get engaged. Shortly before the wedding Qin Su's mother tells Jin Guangyao that his father raped her, and Qin Su is really his half-sister. He's horrified, especially because they already slept together and Qin Su is pregnant. He goes ahead with the wedding but refuses to touch Qin Su again (and may have killed their son to keep the incest a secret). Years later she learns the truth. It ends... badly.
• The incest is averted in Havemercy, but just barely. Word of God has it that the authors had the brothers in question unrelated in an earlier draft, and deliberately included plenty of sexual tension and the possibility of a relationship between them. Later, they decided to take the relationship in a different direction and proceeded to erase all hints of UST between them. They were fairly unsuccessful, though, as most of the readers picked up on it anyway. Since the fact that they're brothers is hidden until near the end of the book, almost all of the readers were already shipping them by default by the time they found out. And once the ship has sailed, well, there's no calling it back to shore.
• In Hearts of Three by Jack London it comes as a salvation for the heroine stuck between two guys for both of whom she cares (and who, moreover, are best friends). She loves one of them more passionately but plans to marry another because they were engaged before she met the other one. Practically at the last moment, her fiancé turns out to be her brother.
• In The Hollow Hills, the second book in Mary Stewart's retelling of the story of King Arthur, Morgause, Arthur's half-sister, bewitches him into sleeping with her, and he only finds out afterward of their relation to one another.
• Max Frisch’s Homo Faber. The novel is mostly just the narrator whining that he really, really couldn’t have known that the young woman he slept with was his daughter.
• I Am Mordred: Arthur didn't know Morgause was his half-sister when he had sex with her.
• In Infandous by Elana K. Arnold, the teenage protagonist has a brief liaison with a much older man. Some months later she's rummaging her mother's closet and finds an old picture of her then-teenage mother with the guy—turns out he's her father.
• Henry Fielding seems to like to subvert this trope for particular effect: In Joseph Andrews, the hero thinks for a while that his childhood sweetheart is his sister; while in The History of Tom Jones, A Foundling, a random one night stand is later seemingly revealed to be the protagonist's mother... Oh NO! Our hero has done something legitimately bad! Fortunately, this is later resolved to be a lie.
• In Kafka on the Shore by Haruki Murakami, the protagonist begins to have a sexual relationship with an older woman who he suspects might be his mother. She denies it, but it is heavily implied both that she actually is his mom and that she already knows this to be true.
• The plot of "Lace" by Shirley Conran revolves around a movie star named Lily gathering four older women (who have been best friends since boarding school), demanding to know which one of them is her mother. As it turns out, one of the women got pregnant as a teenager and had to place her child in foster care, but for various reasons, her daughter ended up lost and she had no way of finding her. As the story is told the reader doesn't know yet who the mother is and since Lily at one point met and deflowered the son of one of her potential mothers you're left to worry that she might have had sex with her half-brother. In the end, it turns out that her mother, Judy, never had any other children so Lily hasn't slept with a sibling. Instead, only Judy realizes the true squick factor. When asked who Lily's father is she lies and claims it was a male friend of the girls, but in truth, she was raped by an Arabic prince and became pregnant. That same Arabic prince later took Lily for a mistress and they spent a couple of years having the best sex of their lives with one another. He never knew she was his daughter and because the affair was public knowledge Judy decided to keep the truth from Lily to avoid traumatizing her.
• In the final Lensman novel, Children of the Lens, it's all but stated that the Kinnison kids (one boy, four girls) will be the progenitors of the Arisians' replacements.
• In the crime novel Lie To Me by David Martin a man kills himself rather messily after finding out that his young wife is really his long-lost daughter. He is particularly distressed by the revelation that she always knew he was her father, but married him anyway.
• In Lirael by Garth Nix, Prince Sameth shows some interest in Lirael, without knowing she's his aunt. At the time she didn't know either, but she's not interested and puts him off by telling him that she's actually thirty-five but has a marvelous skincare regimen. Later, Nick just assumes they're engaged when he sees them together, and when he gets set straight and says she looks too young to be an aunt, Lirael hastily mutters that she's much older than she looks.
• In Lost Souls (1992), Nothing and Zillah begin a sexual relationship and are then informed they're actually father and son; Zillah didn't know he had a son due to abandoning Nothing's mother shortly before she found out she was pregnant, and she subsequently died. Unusually, they continue their sexual relationship even after learning this, which they justify as them being vampires and therefore not subject to the laws and social norms of humans.
• In "The Maias", by Eça de Queiroz, Pedro goes a long way until finding out Maria, the married woman he's been obsessing over, is his long-lost sister (not even half-sister or anything). Not that it matters to him.
• In The Mists of Avalon, a feminist retelling of Arthurian legend, Viviane sets Morgaine up to sleep with her half-brother Arthur as part of a religious ritual. Neither of them recognized the other until after it was too late, and both were suitably freaked out. Viviane can't see what they're upset about.
• In the novel Moll Flanders by Daniel Defoe, Moll unknowingly marries her half-brother (her mother having abandoned her as an infant) and has two children with him. Upon discovering the truth, she dissolves the marriage and flees Virginia for England, leaving her two children behind.
• The Monk: As if raping Antonia wasn't enough, Ambrosio later learns she is his much younger sister.
• Ultimately subverted in The Mortal Instruments. After a first book full of romantic tension, Clary and Jace discover that they're siblings. They spend all of book 2 and most of book 3 angsting about this, until it's revealed that they're not actually related.^note Though granted, Clary's biological dad did raise Jace, so they're Not Blood Siblings who didn't grow up together. Played straight with Sebastian/Jonathan, Clary's actual brother, who kisses her despite knowing full well that she's his sister.
• In the novel The Neighbors by Hannah Mary McKinnon, the teenage children of the titular neighbors have similar interests and may date. Abby, the mother of the girl, Sarah, tries to stop this, as she knows it is possible that Liam, the father of the boy, Zac, could be Sarah's father as well, as they once had a relationship and had a one-night stand the first time they saw each other after that, around the time Sarah was conceived. By discreetly reading Sarah's diary, she discovers that both Sarah and Zac are dating other people. However, when Sarah finds out about Liam and Abby's affair, she blames Abby, and reveals she and Zac are actually dating and have slept together, and she wrote about a fake boyfriend knowing her mother would read it. After the climax, Sarah has broken up with Zac, citing their parents' history as the reason. She doesn't tell him that she secretly did a DNA test and is actually his half-sister, as she loves the man she believed to be her father too much to reveal to him that he isn't.
• In One Hundred Years of Solitude, the biggest fear of the matriarch Ursula is that some of her descendants will be born with a pig's tail, in the fear that it could be the end of both her family and the town. This finally happens a long time after her death, when the last members of the family, Amaranta Ursula and Aureliano Buendía, aunt and nephew respectively, mate and give birth to a pig-tailed baby who is eaten by ants, after his mother dies in childbirth and his father forgot to take care of him because of his deep grief. Both lovers were unaware of their real relation, and Aureliano Buendía only discovers it in the last page of the novel, just seconds before the destruction of the town.
• Orlando Furioso: The warrior woman Marfisa falls in love with Ruggerio and competes with his fiancee Bradamante for his affections. Eventually, they find out that Marfisa is Ruggerio's twin sister who had been separated from him while they were infants. Marfisa apparently took it well and supported Ruggerio and Bradamante's relationship.
• Lydiann Ebersol and Jake Mast fall in love and agree to marry in The Prodigal, the 4th book of the Abram's Daughters series. Unbeknownst to them, Jake is Lydiann’s blood nephew — being the biological son of Lydiann’s (unwed) sister Sadie, who was then adopted by the Masts.
• Pyramids by Terry Pratchett features a pair of romantically inclined half-siblings who eventually figure it out (before getting seriously involved). This one might be a Shout-Out to Star Wars, as the non-related male love interest is a Lovable Rogue smuggler with a Cool Ship. (Also there's a bit of a twist, what with them being royalty in Fantasy Counterpart Egypt, where royalty traditionally marry relatives, so the Morpork-educated brother is probably the only person in the kingdom who has a problem with it.)
• Played with in The Real Thing by Catherine Alliott. Protagonist Tessa has never forgotten her high school sweetheart Patrick, whom her father had forced her to break up with. In the present day her father reveals that he had an affair with Patrick's mother, and Patrick is Tessa's half-brother. Tessa believes her husband's cheating on her, and figures she could start a new life with Patrick - since they've already had a sexual relationship, and her father is too ashamed to tell anyone the truth. Only for her mother to reveal she had an affair as well, and someone else is Tessa's biological father. Tessa's not related to Patrick, although she does have another half-brother, who she knows and also almost slept with.
• In Remember Me, by Christopher Pike, Shari's brother, Jim, is dating a girl named Amanda. It turns out that in fact Jim and Amanda are brother and sister.
• In Repeat It Today With Tears by Anne Peile, the rather disturbed Susie begins an affair with her own father, who abandoned his family when she was a baby. He believes his ex and their children are living in Australia, and Susie gives him a completely fake account of her life so he will never find out. Immediately after he learns the truth he's killed in a vigilante murder by Susie's stepfather, who refuses to believe he knew nothing about it.
• In the novel The Shadow of the Wind, Julian, an illegitimate child who doesn't know who his father is, has a secret relationship with Penelope, the daughter of a rich man who mysteriously decided to take Julian in and pay for his education. It is, however, not until years later, long after Penelope has died giving birth to Julian's child, that he learns that she was actually his half-sister.
• In Sherlock in Love, Sherlock Holmes finds himself falling in love with the astoundingly intelligent and musically-gifted Violet Sigerson. And then finds out that she is his half-sister, due to his mother's marital unfaithfulness. Holmes eventually tries to pursue a relationship, but Violet will have none of it and fakes her death to stop him forever.
• In the Peter David novel Sir Apropos of Nothing, the title character eventually falls in love with the princess he's guarding. But the morning after they've consummated their love...he finds a flame birthmark on her hip, which suspiciously looks like the one on his. Further, it's revealed (though to Apropos only) that the princess is the illegitimate daughter of the Queen and the court jester... and that answers Apropos's question of who his father is, as his mother was raped by a gang of knights... and a shadowy figure that matches the description of the court jester.
• J. R. R. Tolkien's The Silmarillion includes the tale of Túrin Turambar (dealt with at greater length in The Children of Húrin), whose sister Niënor was born after he left the family, causing them not to meet until she, having gone to look for him, has had her memory erased by the dragon Glaurung. Therefore, not knowing who she is, they get married and she even gets pregnant, but then Glaurung spitefully restores her memory in his dying moments, and she promptly commits suicide. Túrin does the same shortly afterwards. Based on the story of Kullervo in The Kalevala.
• In Juliet Marillier's novel Son of the Shadows, the protagonists' sister, Niamh, falls for a druid. When her family finds out, they marry her off in a strategic alliance without telling her that the reason they're so horrified is that the druid (Ciaran) is actually the son of her mother's evil stepmother, thus making him her half-uncle. Oops.
  • Their relationship is later vindicated though. Their daughter turns out to be the child of the prophecy, ending a longstanding feud with Britain over sacred ground. Unfortunately, Niamh never lived to see this, having been pushed off a cliff by the aforementioned evil stepmother when the child was a toddler.
  • When you look at their family tree, Liadan and Bran/The Chief are second cousins.
• A Song of Ice and Fire:
  • Theon Greyjoy's unrecognized tomboy sister practically seduces him until The Reveal to purposefully mess with his head, and see what kind of man he's grown into during their separation.
  • Almost used later when Gendry, who has no clue that his father is King Robert, meets a whore named Bella who flirts with him, all the while bragging that she's the king's bastard. Part of her argument is that she has his famous black hair. Arya (who does not know the truth either) argues that Gendry has it, too, so it's not like it means much. Fortunately for everyone, Gendry's really not in the mood.
• In Orson Scott Card's Speaker for the Dead, Miro discovers his mom was cheating on his (sterile) dad with her old flame Libo, which makes him and his girlfriend half-siblings. Miro doesn't care, but the girl does. Tragedy ensues.
• Josephine Angelini's Starcrossed series plays with this trope twice:
  • Helen is kidnapped by her Missing Mom who tells her that Lucas, her main love interest, is her first cousin. In the next chapter, it's revealed that it's not true, but they spend most of the rest of the books thinking it's true.
  • Orion takes Helen to see his parents so he can explain his past better, and when they look in the house she sees his dad...and her mom. Just as she starts freaking out, Orion quickly explains that it wasn't what it looked like and Helen's mom helps his dad take care of Orion's mom sometimes.
• Happens not once, but twice in The Stone Dance of the Chameleon. Carnelian and Osidian meet in secret and have a passionate affair. Then it turns out that Osidian is the God-Emperor's son, making them cousins, since Carnelian's mother is the emperor's sister. Later, though, it turns out that Carnelian's father is actually the emperor himself — which is not atypical in the ruling house, Osidian's mother being the emperor's other sister. Making them, you know, brothers. In case you hadn't noticed, this is one messed up family.
• Sword Art Online: In the Alfheim Online arc, Suguha Kirigaya, as her toon "Leafa", meets a newbie named Kirito (the main protagonist) and develops a crush on him. She doesn't realize until late in the storyline that Kirito is her live-in cousin Kazuto, and logs out immediately in shock, only coming back when Kirito asks her for her help rescuing his girlfriend Asuna, who was Trapped in TV Land by the Arc Villain.
• In the Tales of the Five Hundred Kingdoms series, the Tradition (a magic force that makes people's lives follow fairytale plots) will allow Brother–Sister Incest only if it's this. If the relatives know each other, they won't be compelled to fall in love even if it suits another Traditional path (e.g. Rescue Romance).
• In Thieves' World badasses Tempus and Cime seem to be laboring under various curses related to this (or effects of mitigators). It seems to have driven them both Ax-Crazy, though in different ways. Some early stories danced around whether they really were related, but Janet Morris' A Man and His God confirmed it.

Live-Action TV

• A common Plot Twist in soap operas is that some couple finds out that they are somehow related. And by common, we mean super common.
• Hispanic soap operas used to love this so much, but it has faded in recent years.
  • The ultimate parody of how this used to be done is the song "María Teresa y Danilo", where a girl, daughter of the aforementioned characters, is forced to cancel her wedding after discovering that her fiancé is the son of her father... only for it to be revealed by her mother that, in fact, she is not his biological daughter.
  • Subverted in one memorable Argentinian case: the main characters find out they're siblings and go their separate ways. As usual, it turns out to be a lie. Only it's actually true... and their father has decided not to tell them. They marry and live happily ever after.

---

• In the 30 Rock episode "The Head and the Hair", Liz and the Hair find out right before kissing that their grandparents are cousins. He seems a little more comfortable with it than she is:
  Liz: Okay, on the count of three, say what level of cousins we would have to be for this to be okay. One, two, three.
  The Hair: Fifth.
  Liz: Unacceptable, no matter what.
• Accused (2023): In "Jessie's Story" it turns out this Kara was so resistant to Jessie and Will growing close, as he's actually her half-brother. Kara obviously feared the two of them might have sex while unaware about this.
• The Affair: Thankfully it doesn't get that far, but when Noah finds himself at A Party, Also Known as an Orgy thrown by a Hollywood producer, he checks out a Two-Person Pool Party before realizing that one of the two kissing girls is his daughter Whitney. He quickly makes himself scarce.
• The 2019 Fox series Almost Family has Julia Bechley rocked to discover her father, renowned fertility doctor Leon, has been using his own sperm to impregnate possibly hundreds of patients over the years. Julia is stunned when a guy she'd had a one-night stand with shows up as his parents had used the clinic, meaning she might have slept with her own brother. Thankfully, he's not although the fact he's married is still a dealbreaker for Julia.
  • Julia brings up to Leon how there's still the chance this could have happened to other people. To her horror, her father just brushes it off as "crossbreeding was a possibility I dismissed" to continue his work and even thinks it would be no big deal.
• Zig-zagged on Arrested Development; Maeby has an on/off relationship with Steve Holt, who is ultimately revealed to be her uncle GOB's illegitimate son (played straight). This prompts the couple to break up, but it turns out that Maeby's mother Lindsay was adopted, meaning Maeby isn't related to Steve after all (subverted), or indeed her other cousin George Michael, who had been attracted to her since the pilot (Inverted). An adult eventually finds out, however, and decides that regardless of who is related to whom the whole thing is just too weird. Zig-zagged again in the Grand Finale, when it's revealed that while Lindsay is also the much younger half-sister of George Michael's grandmother Lucille, meaning George Michael and Steve Holt are half-cousins once removed to Maeby.
• Arrow: Early scenes suggesting a possible spark between Tommy Merlyn and Thea Queen become squicky in hindsight after the Season 2 reveal that they are half-siblings, sharing the same father. Thea had made a pass at Tommy which he rejected because she was like a kid sister to him; when she learns (after Tommy's death) about her true parentage, Thea is understandably freaked out.
  Thea: (to Oliver) You're only my half-brother. You know who else was my half-brother? Tommy. Tommy who I tried to kiss. I tried to kiss my half-brother, who got killed by my real father. That's how screwed up I am!
• As the World Turns: Holden and Lily are one of the show's biggest supercouples. Lily is also the biological daughter of Holden's sister Iva. Who fortunately turned out to be adopted herself so it was not incest after all.
• In a Season 5 episode of The A-Team, "Family Reunion," Face helps an attractive woman come to terms with her fugitive father reentering her life. Afterwards, he tells Murdock that he's going to ask her out after their mission is over because he's never met anyone else he's "felt so at ease with." Murdock starts insisting that she's not Face's type because he and the audience both know, due to dramatic irony, that this beautiful woman is actually his half-sister, and her fugitive father is also his.
• A subtle one occurs in the relaunch of Battlestar Galactica where Ellen Tigh sleeps with Cavil to free Saul. As it turned out, Ellen was one of the Final Five and was essentially Cavil's mother. It was a double-whammy, too. Not only had Ellen viewed Cavil as a son, he was also designed to look like her father. Just another sign of how deep his misanthropy and hatred toward his "parents" really ran. And while Ellen was unaware of this due to amnesia, Cavil knew all about it and deliberately set it up.
• Bored to Death: Jonathon and his girlfriend find out they're half-siblings. Left unresolved due to cancellation.
• Boston Legal: In "The Bad Seed" a young couple know both their mothers went to the same sperm bank years prior and they are the result. They don't know if their mothers used the same donor or not, and it takes going to the lawyers of Crane, Poole, and Schmit to petition a judge to make the bank release just this information. The judge agrees with the claimants need for this information and orders the bank to release just the files on their mothers. Both are shocked to learn they are in deed half-siblings.
• Boy Meets World:
  • In one episode, Eric hooks up with a girl at a combined school rave/parents' anniversary party who turns out to be his cousin. While they didn't get anywhere, he's still thoroughly squicked at the situation.
  • In a more minor example, both Cory and Eric leer at an old picture in their parents' photo album of a sexy young woman in a skimpy wet outfit, only to freak out when they realize it's their own mother.
• In the Burke's Law episode "Who Killed the King of the Country Club?" had the killer trying to avoid this. A new member of the club turns out to have been killed by an elderly woman whose daughter had started dating the man. When the horrified daughter asks why her mother did this as "I loved that man!" her mother reveals "that man was your father!" 25 years earlier, she'd had a one-night stand with a plumber just a month before her wedding. She was thus able to pass off the child as her husband's. As fate had it, the plumber ended up becoming a millionaire to join the club and the woman was terrified he would end up in bed with their daughter. Burke openly asks why she didn't just tell either the truth but the woman didn't want to ruin her own social status with the affair becoming public. She's led off as the daughter can't believe how close she came to bedding her own father.
• Carnivàle: All right, we'll be fair: Justin Crowe wasn't actually aware that he'd made creepy passes at two close female relatives. After all, only his sister-lover actually knew that the new maid was Justin's illegitimate daughter. Not that that necessarily would have stopped him. At all.
• Carnival Row: Jonah is shocked to learn Sophie is his sister, as they share a father, after they've had sex. She already knew and didn't care, invoking her Pharaonic ancestry, since the Pharaohs often married their sisters. He comes around after this, and they stay together, with her even proposing they marry as well.
• Caso Cerrado: One case involves a woman who wants to divorce her husband after learning that he's her paternal grandfather. She was so ashamed that she tried to kill herself. Her grandfather is a musician with at least 26 kids, but he has been in the life of none of them.
• In Champaign ILL, Alfonso meets a girl online after moving back to his hometown. They're surprised they have so much in common during the date. Meanwhile, Ronnie figures out she's his cousin and races to stop them from going all the way. He arrives too late. They keep doing it until Alf joins a sex addicts anonymous program.
• In the sixth season of Community, minor character Garrett gets married to his girlfriend. It's only at the reception after the wedding that they realize Garrett's great aunt and his wife's grandmother are the same person, making them cousins. They decide to stay together anyway.
• The Criminal Minds episode "Taboo" had an interesting take on this trope. The unsub was adopted as a baby by a single mother with a biological teenage daughter. The daughter was hypersexual, thanks to a brain injury, and the boy grew up attracted to her, even spying on her as she had sex with his friends. When she takes him to a lover's lane for privacy, he gleefully makes his move, pointing out that they're Not Blood Siblings, so it's about time for him to get his turn. She then reveals the truth: she's not his sister, she's his mother. The boy snaps, blaming his "sister" and "mother" for turning him into an abomination.
• This becomes a motive for murder on a case in CSI: Miami. Dad had a Secret Other Family, son from Family A met up with daughter from Family B, fell in love, and had a baby together. Then son found out...
• On Dallas, the writers revealed after a few seasons that the Ewings' farmhand Ray was Jock Ewing's illegitimate son, having forgotten that in the beginning of the series, he had been having an affair with Jock's granddaughter Lucy. After realizing what they'd done, they made sure to never reference the affair again, though it was never actually denied to have happened.
• Dark (2017):
  • Jonas finds out that he has been involved in this once he finds out the truth about his father's identity as the time-displaced-to-1986 Mikkel late in season one. However, the other party does not find the truth out until one season later, but this revelation does not stop the two from still having romantic feelings for each other... at least before the older Jonas murders Martha in front of the younger Jonas to ensure his own timeline proceeds as happened.
  • Season 2 reveals that Charlotte's daughter, Elisabeth, is also her mother, meaning that their husbands, Peter and Hanno/Noah respectively, unknowingly married their own granddaughters.
  • Season 3 reveals the same deal to be true of the entire Nielsen/Kahnwald line, as Tronte Nielsen, Ulrich's father, was the son of The Unknown, the son of Martha (Ulrich's daughter) and Jonas (Ulrich's grandson, albeit not the same Ulrich). Meaning their partners all married, or at least had a child with, their own great-great-grandsons, who are also their great-great-great-grandsons, at least genetically. Oh, and Agnes and Noah's parents turn out to be Bartosz and Silja; Silja is Bartosz's half-great-aunt. Confused yet? So is the universe.
• Days of Our Lives:
  • The show had a scene in which Lucas almost has sex with Cassie. They are only stopped when Rex, Cassie's twin brother, arrives and tells them that they are half-siblings.
  • Before that, Cassie had a crush on and kissed her cousin Shawn-Douglas.
  • Long before that in Days, Tony DiMera was in love with a woman named Renee. Unfortunately, it turned out they shared the same father, Stefano, but luckily it soon came out that Tony was really the son of the family's gardener, not Stefano (of course, since this was a soap by that point Renee had married another man...and then got killed by a serial killer...). For long-time fans, this caused a serious amount of squick when years later a retcon made Tony Stefano's biological son, but in the end another retcon made the Tony that had appeared since then his evil doppleganger Andre (long story, naturally) and showed that Tony wasn't Stefano's biological son after all.
• In the Dollhouse episode "Haunted", Echo gets imprinted with the personality of a wealthy woman who wants to attend her own funeral. The woman's son makes a pass at her; she's suitably disgusted.
• This Dutch commercial telling kids not to engage in cybersex has two teens flashing each other over webcams before recognizing the shirts their partner was wearing on the opposite sibling at the breakfast table.
• Dynasty (1981): In an early season three episode, Fallon meets Adam at a bar and after some flirting, the two kiss. The following day, Alexis (Fallon's mother) informs her and Adam that they are siblings. Their relationship doesn't get any better from there.
• Dynasty (2017): For a while, Fallon hooks up with Jeff. It's later revealed that Jeff's mother, Dominique, is Blake's half-sister, meaning Fallon and Jeff are half-cousins.
• In EastEnders, Kareena Ferreira dated family friend Tariq, later making the relationship incestuous when it's revealed Tariq is her half-brother; the family's father had an affair with Tariq's mother. Tariq knew the truth but thought that he could get closer to the family by dating Kareena, taking care to ensure the relationship never became sexual.
• On the British soap Emmerdale Maisie Wylde and Ryan Lamb are caught in bed together and are promptly informed (after many months of hiding this from them) that they are half-siblings. Which disgusts both of them and wind up sending Maisie into rehab and getting their father shot.
• Endeavour: In "Trove", a man performing a Dead Person Impersonation discovers he has just slept with his daughter. The girl had been an infant when he faked his death and stole his commanding officer's identity. The girl had taken her stepfather's surname, so he had no idea who she was. This causes him to vomit.
• Endgame: When the son of the Huxley Hotel's owner goes missing, it turns out that he's gone on a bender because he discovered that the girl he was planning to marry was really his half-sister because his father had had an affair with her mother. Then it also turns out that his mother had been having an affair too, so his father wasn't really his father, and they were unrelated after all.
• ER: A teenage girl is brought in to the E.R. after a fight breaks out at a Jerry Springer-esque daytime tv show. The poor girl had her mother drop one hefty bomb on her. According to the mom, the girl's boyfriend, who she'd been openly having sex with, is actually her half-brother. The girl is devastated because she loves him tremendously and had to be told the terrible news on live TV. Only after the girl commits suicide by jumping off the roof of the hospital do we find out the mother had lied and only said what she said because she wanted to be on television.
• Father Brown: "The Resurrectionists", a pair of lovers turn out to be cousins who never knew that their parents were siblings.
• FBI: Most Wanted: In "Bad Seed", husband and wife Miles and Savannah Maddox were horrified to learn from their DNA ancestry test kits that they are actually half-siblings after being married for three years. What's worse is they also learned that they were the product of their biological father, Dr. Gregory Scanlon, committing fertility fraud who knowingly passed down lupus to his offspring.
• The Fresh Prince of Bel-Air:
  • In the episode, "That No Lady, That's My Cousin", Ashley starts dressing a bit more "mature" to fit in at school, and Carlton doesn’t even recognize her at first when she walks into the lunchroom and is promptly surrounded by boys.
    Carlton: Wow! Will, check out the talent! She’s cool! She’s hot! She’s...
    Will: YOUR BABY SISTER, MAN!
    Carlton: ... (Screams Like a Little Girl)
  • In another episode, this time involving Carlton's older sister, he and Hillary both get into online dating back when it was in its infancy, meaning not everyone had photos attached to their profile. It's not until they both separately arrive at the restaurant that they realize that they've been flirting with each other this whole time.
    Hillary: ...Would you quiet down?
    Carlton: Quiet down? I'M ON A DATE WITH MY SISTER!
    *Everyone at the restaurant looks at them*
    Carlton: It's my favorite country-western song *embarrassed laugh*.
• In Friends Ross and Monica, who are siblings, kissed when both were drunk at a party. However, Monica was half-asleep on a bed and didn't know who that kiss was with, and Ross thought she was Rachel under a pile of coats as it was in a dark room. They only realized it was them years later.
  Ross: You were my first kiss with Rachel?
  Monica: You were my first kiss ever?
  Chandler: What have I married into?
• Future Man: Josh almost has sex with his own mother, having mistaken her for someone else. He finds this out just in time before they get that far.
• Game of Thrones:
  • There's a somewhat squick-worthy one-sided example of this. In Episode 2 of Season 2, Theon Greyjoy returns to his homeland where he meets a young woman and they begin flirting. During a subsequent horseback ride, Theon begins feeling up the woman in a sexual manner (this is the series that led to the phrase "sexposition" being coined) and she not only doesn't object, she seems to take pleasure from it. A few minutes later, Theon (and the audience) get squicked when he learns that woman he was making out with was his sister, Yara, whom he hasn't seen since she was a child, and that she was aware the entire time and played along mostly to see how he'd react in a Secret Test of Character. Needless to say, he failed miserably.
  • As of Season 7, there is sexual tension developing between Jon Snow and Daenerys Targaryen, and it stops being tension when they have sex in the season finale. However, unbeknownst to either of them they're nephew and aunt despite being the same age, as Jon is actually the son of Dany's much older brother Rhaegar. In Season 8, when they find out, Dany doesn't really care about the incest (coming from a dynasty and culture where marriage between siblings was a regular occurrence) and is more concerned that Jon's true heritage means he has a stronger claim to the Iron Throne than she does, as any legitimate child of Rhaegar would be ahead of her in the Targaryen line of succession. However, while Jon has sworn his undevoted allegiance to her and expresses no interest in disputing her claim, he is much more uncomfortable with their consanguinity, rebuffing Dany's romantic advances afterwards.
• On Green Wing, Guy Secretan doesn't find out Joanna is his long-lost and presumed-dead mother until after they've slept together. And it's been caught on tape.
• On Grounded for Life, Lily made out with a guy at the funeral. She later learns he was her cousin. Then she is somewhat relieved when she learns he was a cousin by marriage but squicked again when learning they're cousins by his marriage.
• Throughout Henry Danger, Piper adores Kid Danger and has a huge crush on him, unaware that he is actually her brother, Henry. Needless to say, when she finds out her brother and hero are the same person, she is horrified and disgusted.
• Hollyoaks.
  • Rhys and Beth start dating only to discover they are half-brother and sister. Since everyone knows, they move on to new partners, but then decide to have an affair with each other. It ends very badly when they get arrested and then Beth is killed in a car crash as they try to run.
  • Narrowly averted when Ste meets his estranged father Danny, and heavily flirts with him before finding out they are related.
  • Dodger turns out to be the father of his own twin sister's daughter - they had been separated as children, then met again and slept together as teenagers without being aware of each other's identity.
• One episode of House had a young married couple who both turned out to share the same rare genetic disease... because unknown to the couple, the man's father had slept with the woman's mother and they were half-siblings. On top of that, the half-brother wants to stay together; while the half-sister is disgusted. The episode ends without resolving the situation, leaving the brother/husband hoping that she'll come back while Foreman (who supports the relationship) keeps him company.
• How I Met Your Mother
  • Robin and Barney were on their way to their wedding when they discovered they were related through a mutual cousin named Mitch. By the end of the episode, it's revealed that Robin at least is not blood-related to Mitch, so they manage to avert this trope. They did spend the entire episode awkwardly avoiding any sort of contact though.
  • In an earlier episode, Barney is flirt-dancing with a girl in a disco. But he is only seeing her from behind, and she can't obviously see him at all in this position. Then she finally turns around - and Barney is recognizing his cousin. Quite disturbed, he tells Ted that they must never speak of this again, not even in the form of a funny "Do you remember that time when..."-style anecdote.
• Inspector George Gently: "Gently Going Under" features a half-siblings version. The girl's father had an affair with the boy's mother while her husband was away at the war. When the relationship is discovered, the father tries to move away and take the daughter with him but she is already pregnant. The boy's mother tells her the truth, causing her to attempt to abort the child.
• Just Shoot Me!:
  • Jack's handsome new ex-marine trainer keeps trying to ask Nina out. Nina, who usually Really Gets Around, keeps refusing, much to her surprise. It is at episode's end that she discovers why she's not attracted to him: they're cousins.
  • In another episode an old female friend of Jack's shows up with her son, and he and Maya show signs of being interested in each other. Jack, however, is horrified, because he had a one-night stand right before her wedding and the timing would line up with him being the young man's father. Eventually she reveals that she secretly got a sample of Jack's DNA years ago and tested it, showing he's not the father. By this point, though, Nina's broken the news to the would-be couple, and the man is horrified, so he breaks up with Maya.
  • Jack has Elliot, the magazine's head photographer, take his daughter Maya's new driver's license photograph. The UST between the two leads to a gorgeous photo, which Jack later sees and, not realizing, comments on the beauty of the woman in it. When reminded of his request, Jack takes it well.
  Jack: [Nonchalantly] I'm going to go put out my eyes.
• Kamen Rider:
  • Kamen Rider Double: Phillip is really the brother of Wakana but doesn't know it at the time. He's close to her and plans to leave town with her. Then it turns out that she's really his sister. Once the reveal is made there's no change in plans or attitudes at all (although things change for other reasons) and the audience is apparently supposed to accept that "I care for this girl I know" and "I care for my sister" were exactly the same thing all along. There isn't even a lampshading. Although, to be fair, he never really seemed to think of her that way.
  • Kamen Rider Den-O likewise sank the ship of Ryotaro/Hana^note which already took a massive hit when Hana was de-aged to childhood by revealing that the latter was the former's Niece from the Future. Thanks, Time Travel! They still got off better than the Yuuto/Hana shippers, though.
  • Kamen Rider Kabuto has plenty of Ship Tease for Tendou and Hiyori earlier in the series (with a guest actor who'd played Tendou as a child stating in an interview that he'd been led to believe Hiyori was Tendou's love interest.) However, Hiyori turns out to be a Worm that has copied itself from Tendou's sister, making them siblings. Subsequently, the show dropped any potential romantic arc between them and began having Kagami pursue her instead.
  • Kamen Rider Amazons has Mizuki, who is initially presented as Haruka's foster sister, as his love interest in the first season. It's then revealed that they are genetic half-siblings because Mizuki's mother used her own DNA to create Haruka. The second season subsequently abandons the romantic angle.
• This is played with in Season Eight of Knots Landing. Towards the end of the season, Anne tells Mack that Greg, not him, is Paige's father. Karen and Mack are concerned that Paige may unwittingly be having an incestuous relationship with her uncle as she was dating Greg's half-brother Peter Hollister at the time. It turns out that they need not have worried since Anne was merely being vindictive and Mack is indeed Paige's father. Greg and Anne never had sex, though it wasn't because of any lack of trying on Greg's part. Besides which, even if Greg had been her father, it still wouldn't have been incest since Peter wasn't actually Greg's half-brother, something which the audience knew but Karen and Mack didn't.
• Lady Dynamite has Maria dating a black boy during one of the Duluth scenes. Her dad is against it, so she gives him a speech about the evils of racism - that's when he explains that, during his youth, he slept with the boy's mother during a key party, and might be the boy's biological father.
• Law & Order: Special Victims Unit:
  • Occurred in at least one plotline. The girl was the product of her mother's affair with the boy's father, and when the two began dating due to accidental reverse psychology (the mothers hated each other - the father was in fact the husband of both and living a double-life, known about by one of the wives the whole time), the girl is accidentally killed by her father when he reveals to her that he is the boy's father too. The autopsy reveals that the girl was pregnant when she died and that the boy was the father and that he was related to her. The boy is horrified and vomits in Stabler's office. The boy's mother kills his father when she finds out that he was planning on leaving her for the girl's mother, who was jailed for her part in the myriad crimes going around and with whom he also has a son, the boy's half-brother, and leaving the two new half-brothers without any parent not in prison.
  • A truly dark example in season 19's "Send In the Clowns." A teen goes missing in New York and a butcher is accused of the crime. It turns out she's been having an affair with her music teacher who hailed her genius at the piano. The cops bring them both in as the girl's mother slaps the teacher and starts ranting about his seduction methods with obvious first-hand knowledge. She confesses to her husband she had a one-night stand with the guy...17 years ago. "Do the math." The man himself is utterly horrified and nearly throttled by the husband, and it's reported he's on suicide watch. His daughter's reaction? She's happy because she now knows her father is a musical genius, not "a garbage man", and Benson realizes the girl is deeply troubled.
• In Legends of Tomorrow, after many time traveling adventures, Martin Stein's memories start gradually changing (mostly incoherent) and he repeatedly sees visions of a beautiful woman who isn't his wife. At first, he sadly assumes that changes to history caused him to get together with a different woman. When he finally meets her in the present, it turns out the woman is his daughter (he didn't have any children before history changed).
• The end of the episode with the Pimp Hat in Less Than Perfect had Owen and his Distaff Counterpart date reveal that one of the many things they had in common was that they both had donor dads who were artists. Claude pulls him aside to tell him that it was very likely they were brother and sister. He retorts that "this couldn't wait until tomorrow?", meaning he wasn't completely against the incest.
• In Lewis Brother and Sister twins that were adopted by different families meet, fall in love, and marry. When they can't have kids, the couple gets genetic tests done. They find out not only that they are related, but they both have the markers for Fatal Familia Insomnia. They track down their birth mother but get Dr. Dobson's name because their mom used it. They are slowly going insane from lack of sleep.
• Lost Girl:
  • Bo gets hit on and kissed by a woman who turns out to be her long-lost mother Aife (Bo and her mother are succubi and don't age).
  • Later in the show, Bo meets and has sex with Persephone, wife of Hades, only to learn after the fact that Hades is her biological father, thus making Persephone her stepmother.
• In one episode of The Love Boat, a woman comes on board with her son, to meet the daughter she gave up for adoption. Before they all get together, the son and the daughter meet, and, not knowing who the other is, they fall in love and have sex. The daughter is freaked out when she meets the mother and discovers who the guy she slept with is. Fortunately the son is actually the mother's step-son, so the couple aren't blood siblings and can get married, but the mother has no idea how she'll phrase the wedding invitations.
• On MTV's late-night, sex-advice talk show Loveline, a man called in asking what to do after discovering his pregnant girlfriend is his half-sister (his mother was estranged for years and the girl was racially-mixed, so he had no idea at first).
• In one episode of Malcolm in the Middle, Reese finds Lois's high school diary, thinking it belongs to a schoolmate he's never met. After reading it he develops a crush on the mysterious girl, until Lois sees him with it at the end of the episode. Needless to say his fantasy of kissing her goes in a different direction.
• A Mad TV sketch parodying Korean Dramas ends with the main character and his love interest learning they share the same mother.
• In the season 2 finale of Married... with Children, Kelly learns everyone in her mother's hometown is related, even a guy she had sex with. Her response is immediate Brain Bleach.
• The Mick: Chip meets his biological father after learning about him, and finds that his half-sister is attracted to him. She kisses him, although Chip tries to resist this, and he stops things after she does. Subverted though later when it turns out they don't share a father.
• Midsomer Murders:
  • In one episode, a man had 'spread his seed far and wide'—you could hardly turn a corner without finding one of his bastards. One couple didn't meet until they were both in graduate school in Canada and got married, only later realizing they were half-siblings; she was squicked, he didn't mind. It's also been used in several other episodes.
  • Inverted in "The Creeper" where two childhood friends clearly like each other, but don't act on it because they believe they're half-siblings. (His parents were having trouble conceiving, and her father agreed to sleep with his mother to get her pregnant, but his mother's husband — who was okay with this — would be the father legally speaking. The kids were told when they were old enough to understand.) The investigation of that episode's murder leads to the revelation that his mother was also having an affair behind both men's backs, and her paramour was actually the kid's real father. Both friends are stunned, but admit they're sort of relieved they're not related after all, and the last scene heavily implies they've hooked up.
  • "Master Class" has a young woman almost hook up with a much-older man who is not only her father, but also her grandfather, and he sought her out on purpose. (It turns out to be part of some crazy eugenics scheme on his part.) Fortunately, Barnaby reaches her and informs her before anything happens.
  • In "Dark Secrets", a woman learns the younger employee she's been sleeping with is actually her nephew and is violently sick. Said young man doesn't react as much, because he's still under the shock of learning that he's the product of Brother–Sister Incest.
  • In "The Killings of Copenhagen", Harry Calder is in love with (unbeknownst to him) his real half sister, Summer Haleston, who came to the town to met her real father, Eric. She does try and push him away knowing this, but after being questioned by the police she tells him. He is upset, but the problem was his fault not hers.
  • In "For Death Prepare", Phoebe Whittingdale and Luke Dunlow become attracted to each other and plan to leave their village to travel the world. But one of the problems they face is Luke's father, Marcus, acting like he's creepily attracted to Phoebe while also trying to prevent Luke from leaving with her. At the end, Marcus explains what's really going on: he once had an affair with Phoebe's mother nine months before she was born and he always wondered if he was her biological father. Once Luke became attracted to her, Marcus broke into the local medical clinic to learn her blood type which ultimately confirmed his suspicions that he is indeed. Hence why he'd being trying to break up their relationship and also get to know her.
• In Mr. Robot, Elliot's fellow hacker Darlene is unusually close to him. She knows where he lives, seems to have little boundaries with him, and is unusually concerned about his safety for someone he barely knows. When one of their hacks is successful and Darlene congratulates him and tells him she "loves [him] so much", Elliot kisses her, which causes her immediate disgust and she asks if he's forgotten who she is. Turns out, she's his sister and Elliot, who has a number of mental issues, has forgotten this.
• In Murder, She Wrote: The Celtic Riddle, it's never actually spelled out, but it seems likely that the reason Eammon was a benefactor to Paddy was that he suspected Paddy might be the long-lost son he wanted to make things up to, and this is also why he disaproved of Paddy dating his daughter. Luckily it's subverted, as the "Lost Boy" turns out to be someone else.
• Referenced in My Name Is Earl. Joy never told her parents that she divorced Earl and married Darnell because she believes her father is a racist since he wouldn’t let her date a Black boy in high school. It’s later revealed that he had numerous affairs with Black women throughout the years, and don’t want her dating that boy because he was probably her half-brother.
• In The Nanny, Fran finally meets a guy who seems absolutely perfect for her: Jewish, a doctor, and understands her. At Fran's cousin's wedding, they see each other, and kiss. Cue Fran's mother...
  Sylvia: Isn't that adorable. Let me get a picture of you and your cousin Bob.
  (Fran and said cousin immediately jump apart, looking thoroughly Squicked)
• NCIS season 6 episode "Heartland" had the team go to the mining town of Stillwater (coincidentally Gibbs' birthplace) where it was revealed the hospitalized Marine and his childhood friend, who remained in Stillwater waiting for him, shared the same father unbeknownst to them both. Though she maintains that their relationship was strictly platonic, they did have feelings for one another.
• Defied in New Amsterdam (2008). The immortal protagonist John, who is very much capable of having children by mortal women, keeps track of his family tree specifically so he can avoid getting into a relationship with someone who might turn out to be related to him.
• Averted in The New Mike Hammer. Mike meets an attractive woman with the assumed inevitable bedding. However she tells Mike that before he takes her upstairs he needs to know something. Mike however has already realised she's a daughter he never knew he had.
• Nip/Tuck: In season 5, Christian finds out that he fathered a daughter when he was in college. She just happens to be Matt's new girlfriend (who was raised as Sean's son, but is actually Christian's).
• The Outer Limits (1995): In "Last Supper", Frank worries that Jade is his daughter, since he had sex with Laura, who he's sure has to be her mother due to their resemblance, around the time she would have been conceived. She's in a relationship with his son from another woman, so he's afraid the trope is in play. However, it turns out that Laura and Jade are really the same woman.
• On The Outpost, Janzo has spent most of the second season bantering and flirting with handmaiden Naya. They finally share kisses while locked in a cell alongside Jazo's mother, the Mistress. Naya tells of her mother and as soon as she hears the name, the Mistress starts laughing "know her? I sold you to her!" She then spells out how Janzo has just been making out with his twin sister. Poor Janzo nearly has a full breakdown and Naya isn't much better.
• Red Dwarf:
  • It was revealed that Lister's ex-girlfriend Kochanski is actually his mother. In the next series, Lister still uses a sexual-magnetism virus to seduce her in an elevator despite his knowledge of this and it nearly works. Then again, Lister also discovered at the same time that he was his own father (via in-vitro fertilization), which probably trumps any genetic relationship concerns.
  • Anticipated by Rimmer in "Back To Earth"; After telling the creator to create for him a beautiful, adoring girlfriend, he quickly adds that she should NOT turn out to be his long-lost sister.
  • The novelization Better Than Life has Rimmer's second wife turn out to be based on a younger version of his mother. He can't even complete the thought when he realizes it, he's too disgusted and horrified.
• Riverdale: Some time after Jason Blossom was murdered, Polly Cooper reveals she had been sleeping with him and is pregnant. Her father Hal goes nuts and demands she get an abortion. The rest of the family assumes this is because the Blossoms and Coopers are Feuding Families, but Hal reveals that his grandfather was the brother of Jason's great-grandfather, but estranged from the Blossom family and changed his last name to Cooper, which is what started the feud in the first place. This means that Polly and Jason are third cousins. Polly decides she doesn't care and will carry the pregnancy to term.
• In Scrubs when JD's girlfriend gets pregnant, they discuss the situation and JD is opposed to adoption because he fears this trope may occur if they have a daughter.
• On Shadowhunters, after an entire season of flirting, kissing, and overall developing strong romantic feelings for one another, Jace and Clary find out they are actually brother and sister in the episode "Blood Calls To Blood", from the mouth of Clary's father Valentine (later confirmed by Clary's mother). Actually, Valentine lied: Jace is the child of a different pair of Shadowhunters altogether, whom Valentine raised to compare with Clary's actual biological brother Jonathan (and telling Mom that Jace was Jonathan). On those grounds, Jace and Clary resume their relationship late in season two.
• On Smallville, when Clark meets Kara (aka Supergirl), they seemed a little attracted to each other. When Kara's comment about her father Zor-El causes Clark to realize that they are cousins, he backs off, clearly (and understandably) disappointed.
• In season 3 of Sons of Anarchy it is revealed that Jax Teller and Trinity Ashbey are both John Teller's children. Ony a few people know of this and since Jax lives in California and Trinity in Northern Ireland they do not see the need to tell them. When Jax comes to Ireland he and Trinity quickly hit it off and are about to have sex when their mothers walk in on them.
• One episode of Superstore plays this as a joke when Justine and Marcus discover they share a cousin, then quickly realize they should stop hooking up (which was also a reveal).
• Taskmaster: in the barrage of Narmy tropes engendered by the "most suspenseful soap opera cliffhanger" task in "A Coquettish Fascinator," Jess and Kerry build this into their entry, "Cul-de-Sac":
  Kerry: He's the best I ever 'ad, Donna!
  Jess: (dramatic inhaler puff) You can't be with him, Donna!
  Kerry: Why?!
  Jess: 'Cause you're his mum!
  (melodramatic organ music, Kerry pukes)
• An unusual example in True Blood: Vampire Bill, turned in the 1800's, finds out his human squeeze Portia Bellefleur and other members of the Bellefleur family (recurring characters in the series) are descended from his human daughter, and are thus his descendants. Bill is far more grossed out by this than Portia. She is perfectly willing to continue their sexual relationship, citing logical reasons why this shouldn't affect them: they're consenting adults, vampires (in this setting) can't produce children, and even if they could, Bill and Portia are as genetically similar as perfect strangers. Nonetheless, Bill is simply too uncomfortable to continue a relationship with his great-great-great granddaughter, so he glamours her into being utterly terrified of him just so she will leave him alone. The one upside is that Bill develops an Odd Friendship with Portia's brother, Sheriff Andy, due to his ability to act on Bill's legal behalf as his living heir, with the bonus that Andy isn't trying to sleep with him.
• Two and a Half Men: After talking to Charlie's latest piece of ass Gloria, Evelyn goes out of her way to stop her and Charlie from sleeping together. Right before they're about to do the deed, Evelyn brings over Gloria's mother and they explain that they each slept with the other's husband shortly before the mother got pregnant, and that there's a chance that Gloria and Charlie are half-siblings. This puts Charlie off, but Gloria still wants to screw him.
• The Untamed: Like in the novel, Jin Guangyao and Qin Su get engaged before either knows they're half-siblings. Unlike in the novel, Qin Su isn't pregnant before the wedding. Her mother still tells Jin Guangyao the truth... and then he marries her anyway. And has sex with her when he knows she's his sister. Qin Su only finds out years later, and she's so horrified she kills herself.
• In Veronica Mars, Duncan Kane broke up with Veronica because his mother told him she was his half-sister. After the first season finale revealed Veronica and Duncan weren't related, they got back together (until Duncan got Put on a Bus).
• In Wayward Pines, Jason Higgins finds out that the woman he has been having a relationship with, Kerry Campbell, is actually his mother. The two lovers are around the same age because Kerry was unfrozen many years after Jason.
• The Korean soap opera Winter Sonata is Marmalade Boy if Yuu went missing, got amnesia, and really is half-siblings with his love interest. Well, in fact he could be instead the half-sibling of his love rival, but the soap just was happy toying with that until the last chapter.
  • There is a memorable scene in this drama where one of the rivals, after being clued of the above situation and arguably tired for the on-off situation who has already left her out of the game, ends yelling to one part of the conflicted couple "It doesn't matter if you are really siblings or not, just go out of the country and marry anyway! Abroad nobody is going to know!".

Music

• The Merry Wives Of Windsor: "All the Lads in Town" is about a girl who discovers that her father's roving ways have resulted in her suitor — and, in fact, every eligible lad in her town — being her half-brother. She despairs that she'll be forced to remain an unwilling maiden all her life, but at the end her mother tells her that she was actually fathered by a passing sailor and as such is free to bed who she will.
• Sia: The song "Butterflies" plays this on the listeners. It sounds like just a regular song about lingering awkwardness in a relationship, until the very last line right at the end of the song, when she casually remarks "Because we came from the same cocoon".
• "Weird Al" Yankovic: The second verse of "A Complicated Song" provides the page quote. After discovering his girlfriend is his cousin, the narrator wonders if he should still stay with her, have inbred kids with 11 toes, and "move to Alabama where that kind of thing is tolerated".
  I was feelin' pretty down
  'Til my girlfriend came around
  We're just so alike in every way
  I gotta say
  
  In fact, I just thought I might
  Pop the question there that night
  I was kissing her so tenderly
  But woe is me
  
  For who would have guessed
  Her family crest
  I'd suddenly spy
  Tattooed on her thigh?
  And son of a gun
  It's just like the one
  On me

• Gothic Americana might not exist as a genre without this trope. Slim Cesna's Auto Club has an EP named "Crossbreeding Begins at Home." Similarly, about half of Jay Munly's oeuvre seems to rely upon this trope. If you're curious, look up the lyrics to "Big Black Bull Comes Like a Caesar" and "There's a Goose Walking Over My Grave."
• In the folk song "I'm My Own Grandpa," the narrator marries an older woman with an adult daughter. The narrator's father then marries the daughter, making the son's stepdaughter his stepmother. Because the narrator is married to his stepmother's mother, he has become his own step-grandfather. Not actually incest, either.
  • A real life example was avoided when Mandy Smith's mother broke up with Rolling Stone Bill Wyman's son. Smith and Wyman were married at the time, giving Smith a narrow escape from becoming her own step-granddaughter-in-law.
• Cornelis Vreeswijk's Incestvisan (Incest Song) has a similar structure an example named above: Boy meets girls, falls in love. Dad intervenes, claiming they are his sisters. Boy then talks to mom, mom: "Oh, don't worry, he's probably right but he's not YOUR father anyway..."
• The folk song "Johnny Be Fair" parodies this. The female narrator repeatedly falls in love with men, only for her father to pull out the Parental Marriage Veto because he's their father too. In the end, she goes to her mother, who says "he's not really your father, marry anyone you want". It dates back to Elizabethan times and probably further.
• Frank Zappa's "Magdalena" is a lengthy and detailed confessional by a Canadian maple syrup salesman to his teen-age daughter of what he'd like to do to her.
  • There's also "Brown Shoes Don't Make It", with this exchange, repeated three times:
    Man: If she were my daughter I'd...
    Girl: What would you do, Daddy?
• Harry Chapin's "The Mayor of Candor Lied" is a particularly bone-chilling twist on this one: boy meets girl, girl's father disapproves, ostensibly because the boy is poor. Boy catches his mother with her father and blackmails him into letting boy and girl be together. Then her father takes her overseas on vacation and doesn't bring her back, and in the ensuing confrontation, the boy suddenly notices how much the girl's father looks like him...
• Tom Lehrer wrote a jaunty, upbeat "theme song" for Oedipus Rex.
  When he found what he had done, he tore his eyes out, one by one. A tragic end to a loyal son who ... loved his mother.
• Shame and Scandal subverts this: This young man discovers his dad is also the father of every single one of his girlfriends then learns from his mother that his "dad" his not his real father.
• The big reveal of Type O Negative's "Stay out of my dreams" is this trope.
  With your straight black hair and emerald green eyes
  Hippies pointing "that's Pete's sister in disguise"
  Maybe you had uttered those words as a jest
  I don't mind the allegations of incest
  At the time I thought I could love no other
  Till I heard you say that I was your brother
  In your e-mail said how much we look like twins
  How it turned you on just knowing it's a sin
• The song "Son Don't Go Near the Indians" — The whole time the main character of the Western song is told "Son don't go near the Indians, please stay away." Reverse psychology plays its part, and he goes near the Indians — a lot. He falls in love with a girl there about his age. Near the end, they resolve to get married. Only then does his father explain that his actual son got killed by the Indians, so he stole one of their baby boys, the protagonist, and that his girlfriend is his sister. "And that's why I've always said — 'Son, don't go near the Indians, please stay away'"
  • Subverted in the related song (most likely a parody) "Son Don't Go Near the Eskimo" which leads the listener to suspect a similar conclusion, making the big reveal (the girlfriend is not his sister, but she has "the coldest nose in Alaska") somewhat anticlimactic.

Myths & Religion

• Oedipus' story in Greek Mythology involved him unknowingly marrying his own mother Jocasta. They only learned the truth years after having four kids together. Neither reacted well, Jocasta killed herself while Oedipus put out his own eyes. Told famously in the tragedy Oedipus the King. Despite the way this actually plays out, Oedipus somehow ended up as the Trope Namer for Oedipus Complex even though he's not an example of that.
• Averted with Telephus. He was given a beautiful woman named Auge by a king as a reward for winning a war. Suddenly, just as he gets ready, a Bolt of Divine Retribution flashes between them. Surprised, they start talking... turns out Auge is his mom, while his father is Heracles, who was apparently the one to send the lightning. Mind you, in some versions, the trope averted wasn't Surprise Incest but Offing the Offspring - Auge still loved Heracles, so she brought a Chastity Dagger along.
• Finnish mythology: Kullervo from The Kalevala seduces a girl he meets on the road. When they find out she is his own sister who he never met, the girl commits suicide.
• Norse Mythology:
  • In The Saga of Hrolf Kraki, King Helgi of Denmark marries the servant girl Yrsa whom he kidnapped on a viking raid to Saxony. It eventually turns out she is his own daughter he conceived by rape on an earlier raid.
  • In The Saga of the Volsungs, Sigmund sleeps with a vagrant soothsaying woman. Many years later, Sigmund learns the soothsayer was his sister Signy in disguise, and her son Sinfjotli who Sigmund thought was his nephew is actually (also) his son.
• Vietnamese folk tale of Tô Thị: The titular woman accidentally married her long-lost older brother and produced a healthy son with him. When the husband found out, he left the family forever without telling them the truth. Tô Thị and her son longed for him until they both turned to stone.
• In Russian, a few species which produce different-colored flowers on the same plant are collectively known as John-and-Mary (Иван-да-марья). The legend behind the name is that two siblings by these names were separated during a Mongol raid and made slaves. After growing up, they met, fell in love and married, but then the relationship was revealed, and they desperately prayed to God that he would allow them to remain together somehow. Hence the flowers.
• Arthurian Legend: In the most famous version, Mordred is the result of an affair by Arthur, who grew not knowing his biological family, and his half-sister Morgause.^note Though in older versions, Mordred's father was Morgause's husband Lot. Neither realized they were siblings, though modern versions sometimes make it so that Morgause is evil and just didn't care. She might also be switched out with Morgan le Fay, Arthur's other half-sister.
• In the Irish mythological text The Wooing of Étaín, High King Eochaid is tricked into sleeping with his own daughter as punishment for his transgressions against the Sídhe. Overcome with shame, he orders the child of their union to be killed by being thrown to wild beasts, but she is rescued by a passing herdsman and grows up to be Mess Búachalla, mother of High King Conaire Mór.

Oral Tradition

• There's an urban legend about a married couple who keep having children with some rare deformity, like an unusual number of fingers or toes. When a doctor tells them it might be the result of inbreeding, they get nervous because one of the couple was fathered by a sperm donor. Sure enough, it turns out that said donor was the other half of the couple's dad (usually said to have given his sperm to pay his bills or buy a car in college), meaning the two unknowingly had the same father.

Podcasts

• Random Assault: The other hosts claim Drew has a lot of surprise sex with his 2 younger brothers.

Theatre

• August: Osage County. Little Charles and Ivy have a Kissing Cousins relationship, which is made worse when it's revealed that Little Charles is actually the biological son of Ivy's father, making them half-siblings as well.
• "Emmeline": In which the eponymous 19th century New England woman has an illegitimate son who is taken away from her just after birth. The son is given up for adoption and raised by a family in Ohio; Emmeline, meanwhile, saw the baby for such a short period of time, she is easily convinced by relatives that she had a daughter, not a son. Twenty years go by, and Matthew, a handsome young laborer, appears in Emmeline's hometown. They unwittingly fall in love and marry. Later, a member of Emmeline's extended family shows up to attend a funeral, and, while there, recognizes Matthew as the child Emmeline gave up long ago. After this earth-shattering reveal, Emmeline is abandoned by her son and made to be a pariah in her community, where she lives the rest of her life in miserable isolation and shame.
• Subverted in the Forbidden Broadway parody of Spring Awakening:
  Mother: Oh, God! What have you done!
  Wendla and Melchior: Mother! (To each other.) That's my mother, not yours. Stop doing that! (To Mother.) Mother!
  Mother: Actually, I am both of your mothers.
  Wendla and Melchior: Both? But that would mean... eeew!
  Mother: Let me explain. In some scenes, I am Melchior's mother, and in others, I am Wendla's. I also play a piano teacher, and when I wear this hat, I'm Frau Knuppledick. Four different characters, all wearing the same dress.
• In A Funny Thing Happened on the Way to the Forum, Philia is a virgin slave-girl arranged to be sold/married off to Miles Gloriosus, the Roman general responsible for having destroyed the land where she grew up. She is somewhat reluctant to marry even before she falls in love with Hero. But everything ends happily when a set of matching rings proves Miles and his prospective bride are long-lost siblings, enabling the hero and heroine to marry.
• In Henrik Ibsen's Ghosts Regine turns out to be Oswald's half-sister. When the secret is finally revealed, she is not that upset about having tried to seduce her own sibling and more angry about being brought up in a lower social standing than him. Her first concern is to go get her rightful inheritance.
• In Carlo Gozzi's The Green Bird, King Tartaglia unknowingly almost marries his own daughter Barbarina. Thankfully, the titular bird reveals the truth to them before the wedding takes place. Since Tartaglia's first wife turns out to be alive and the green bird is actually a cursed prince in love with Barbarina, no hearts stay broken.
• Played with in The Guilty Mother, the unpopular Downer Ending segment of the Figaro trilogy. Both lovers are not the biological offspring of both of their legal parents, and Figaro has to juggle their Who's Your Daddy? plot so that they can marry and nobody needs to be publicly disgraced.
• In The Importance of Being Earnest, it's revealed that Jack and Gwendolyn are long-lost cousins. In keeping with the time and place in which the play is set, this is not what destroys their relationship but rather what allows them to marry, since being Gwendolyn's cousin means that Jack is now known to be of the proper social status to marry Gwendolyn.
• In The Marriage of Figaro, the character interested in marrying Figaro turns out to be his mother, and says something like she always loved him — just in the wrong way previously.
• It's never particularly dwelt upon (the woman in question dies minutes after announcing the fact, and everyone has more imminent problems to worry about), but towards the end of Leoš Janáček’s The Makropulos Affair it's revealed that all the time Albert Gregor has been vying for the love of his great-grandmother.
• The Roman comedy trope used in A Funny Thing Happened on the Way to the Forum was used more seriously in Gotthold Ephraim Lessing's play Nathan The Wise—the title character is Jewish and it is revealed that his daughter is actually not a blood relative. He is charged with the crime of raising a Christian as a Jew. It turns out that she is the sister of a literal and celibate Knight Templar in play (taking the place of the mercenary of Roman comedy), who other characters had been trying to fix her up with. Both of them turn out to be the children of Saladin's brother and a Christian woman, and in at least one translation, the Templar expressed gratitude at the news, as he was not yet prepared for sexual love.
• Thomas Middleton's 1611 play No Wit, No Help Like a Woman's plays with this trope: one subplot features a young married couple who are horrified to find out they're actually brother and sister, and then quite relieved to discover that the girl was in fact switched at birth so they're not related at all.
• The story of Oedipus who unwittingly married his own mother is the subject of Sophocles' Oedipus the King.

Video Games

• In AI: The Somnium Files, shortly after meeting Date, Iris seems to be immediately attracted to him and even strongarms him into taking her on a date. Although Date doesn't truly reciprocate, being more than a decade her senior, he does admit that she is cute and he seems to still be attracted to her body. However: Thanks to body swap shenanigans, it ends up being incestuous in two different ways. Firstly, Date's mind and personality are, unbeknownst to him, that of Iris's mother's former boyfriend, a man who, despite their lack of blood relation, Iris fully thinks of as her father. Secondly, the body Date is currently inhabiting is that of Iris's half-brother, Saito. Thankfully, once the truth comes out, Iris fully drops her pretenses and instead begins pressuring Date and her mother to properly get married. Iris still bugs Date for a "date," but it's clearly in a father/daughter sense at that point.
• In the Baldur's Gate series, Imoen and the main character (if he's male) have the sort of sorta flirty relationship you'd expect from lifelong friends of opposing genders. For that matter, if the main character's female they have the sorta flirty relationship you'd expect from lifelong friends of that sort. When Baldur's Gate II was released and Imoen was not one of the characters with whom you could pursue a romantic relationship, a lot of fans of the original were very surprised and rather disappointed... until you found out that Imoen was your half-sister.
  • This is actually brought up in Baldur's Gate II: Throne of Bhaal if the main character's male. Viconia insists to Imoen that given the number of times he's saved her life, she should serve him in every way. Imoen acts squicked and cites why. Viconia brushes it off, pointing out that the common heritage would hardly one of blood. Imoen then notes that — canonically by that point — the main character has saved Viconia's life at least twice...
  • Some people did a mod that allows this relationship; the Imoen Romance mod for Baldur's Gate II is alive and well, and is widely known for near-total freedom of choice in the protagonist's options. Imoen is romanceable by both males and females, and to the mod's credit, does not shy away from the incest issue — Imoen in particular has issues with it.
• In Crusader Kings II it's possible for a cheating wife to pass her paramour's child off as her husband's, which the game keeps track of in an invisible character stat. It is, therefore, possible to betroth someone to their secret half-brother.
• In Duskwood, there's a one-sided variant between Hannah and Jake, the hacker who contacts the player. They're half-siblings, unknown to her but known to him. Having no other family, he reached out to her a few years before the game begins, wanting to connect. The thing is, he didn't tell her they're related, with his reasoning being that he didn't want to cause strife in her family, as his existence is the result of Hannah's father cheating on her mother. He was content to just be friends with no familial connection, but Hannah, unaware of the truth, fell in love with him. When he realized, he quickly distanced himself from her and finally cut all contact.
• In Fallout 4, you learn that all 3rd Generation Synths are created using DNA from your baby, Shaun. This turns a romance with Curie, Magnolia or Paladin Danse towards this trope.
• In the Fate/Grand Order event "Murder at Kogetsukan", Harriet Violet resorted to murder to prevent this. Juliet and Eva were unknowingly the result of her one-night stand with Aaron Goldie, so Juliet couldn't be allowed to marry either of Aaron's sons. She was so paranoid that the mere knowledge of the affair would result in a full-out war between the crime families that she refused to even explain the matter to said sons when they questioned her about her motives, which results in her killing them when they rather understandably don't see what the problem is and refuse to call off the engagement.
• In the Fire Emblem franchise:
  • In Fire Emblem: Genealogy of the Holy War:
    • Seliph and Princess Julia seem instantly attracted to each other upon meeting, but it turns out that Julia is Seliph's inbred half-sister, as Seliph's mother Deirdre was brainwashed and forced to breed with her half-brother Arvis (who had no idea that they were siblings). There's a reason that the game's Relationship Values system won't allow them to be paired—unless you exploit a programming glitch.
    • In the first half, Claude's most popular pairing is with Sylvia, who is hinted to be his long-lost sister, but said by Word of God to be a distant cousin.
  • In Fire Emblem: Awakening it was implied that Lissa was smitten with a man posing as Marth who had saved her from Risen. Keep in mind, that Marth is her distant ancestor, but it turns out that 'Marth' was actually Lissa's niece from the future.
  • In Fire Emblem Fates, the Male Avatar gets a nice dose of Ship Tease with Azura...and then the Golden Path reveals they're cousins. And since The Reveal doesn't occur until almost the end of the game, there's a solid chance they'll be married at that point. Given the medieval-esque setting, though, and how neither seems to particularly care about the relation if they are married, marrying one's cousin is probably seen as an acceptable thing. And note The Reveal only happens extremely late in the Golden Path: they could theoretically marry in any of the paths, meaning in two of them they never find out they're cousins.
• In the first Killer Instinct game, Black Orchid has a finishing move where she unzips the front of her outfit and flashes her breasts to her opponent, causing male characters (including Jago) to pass out in excitement. At the end of the game, she learns that Jago is her long lost brother.
• Used in No More Heroes when Travis is informed that his ex-girlfriend Jeane, who he did sleep with, was his half-sister, which she knew beforehand. He reacts appropriately.
• Octopath Traveler II has a fairly minor yet also very spoiler-y example in Throné's story. Scaracci implies that he's attracted to Throné in her first chapter and asks her to "help him out" using her hands. Throné immediately picks up on the innuendo and is annoyed by it. Fortunately, it goes nowhere, since her final chapter reveals that most (if not all) of the criminal orginization they're a part of are half-siblings with the same immortal father.
• Sailor Moon: Another Story: George and Mary, a minor couple that Sailor Jupiter helps get together in her chapter, at the end get revealed that the reason why their fathers are so angry at each other, is because George's father eloped with the younger sister of Mary's father, making them cousins.
• All over the place in the 0verflow universe (which School Days is a part of), thanks to the omnipresent patriarch Tomaru Sawagoe banging a lot of women (even those related to him) and maintaining his secrecy in regards to his kinship with many characters. As a result, a lot of characters who are in romantic or sexual relationships share a familial connection that can be traced back to the Tangled Family Tree that he has made. One prominent example would be Makoto with Sekai & Setsuna, who are AT BEST half-uncle and half-nieces thanks to the former being Tomaru's son with one of his nurses and the latter two being Tomaru's granddaughters with other relatives^note For further context as to how horribly inbred their babies are, here's the rundown: Tomaru and his half-sister Moegi are the parents of Kagura and Youko. Tomaru also impregnated Kagura's friend Hatsuka with a son named Shun. Shun ALSO Really Gets Around and has fathered several of the heroines, including Sekai who is his daughter with Youko. Setsuna is Shun's daughter with Mai. Mai happens to be one of the many children Tomaru sired by Kagura, his daughter/half-niece. And while the canonical family tree only confirms that Makoto gets Sekai and Setsuna pregnant, there are routes in Shiny Days where Youko and Mai have his babies too.
• In Shadow Hearts: Covenant, the hero Yuri meets the babealicious Karin and the two go through many harrowing adventures together. It becomes clear pretty quickly that Karin is falling for Yuri, although he's still pining over his lost love from the first game in the series. However, at the end due to some messing around with the space-time continuum, Karin ends up traveling back in time and marrying Yuri's father...and becoming Yuri's mother. Good thing they never actually got together, eh? This makes sense in a twisted way. Considering that Yuri and his father were apparently very similar people, it does make sense that Karin first falls for Yuri in her time and for his father in the past. While they only remained friends, Yuri does manage to convince Karin to wear a very skimpy outfit. The scene becomes either squicky or more hilarious afterwards depending on how perverted your sense of humor is.
• In the PS2 adventure game Shadow of Destiny, with Eike and Dana living happily ever after, despite secretly being biologically father-and-daughter, in Ending E.
  • Well, there's a reason why it's one of the worst endings. And Dana seems to be at least subconsciously aware of the connection on some level and is bothered by it.
• In Shin Megami Tensei II, for most of the story, there's plenty of Ship Tease between Aleph and Hiroko. Later, it is revealed that Hiroko's missing son that she was looking for since the beginning of the story was actually Aleph all along. Aleph was a genetically-engineered Artificial Human created by The Center and Hiroko was selected to be his surrogate mother. Due to his altered biology, he aged very rapidly to the point where he appeared to be the same age as Hiroko when they first met.
• Shows up occasionally in works made with The Sims 2: unattended children can be taken away by a social worker, and then adopted into a different family. The adoption code deletes the family connection to the birth parents and creates one with the adoptive parent(s). Some players have used this loophole to have siblings or even twins, adopted into different families, strike up romances. Since there's no genetic penalty for incest, they can even have kids. Read all about it.
• One of the big twists in Twelve Minutes is that the husband and wife are really half-siblings (which the husband finds out after impregnating her). The husband suppressed the knowledge and it only came out after getting stuck in a "Groundhog Day" Loop.
• Umineko: When They Cry: Sayo discovers their true identity as Kinzo's bastard Parental Incest Child by Rape, putting their attraction to Battler, George, and Jessica firmly in this trope.
• At the end of the True Pacifist route of Undertale, the married dog couple Dogamy and Dogaressa are briefly concerned that their parents having merged into an Amalgamate might technically make them siblings. They conclude that since they're dogs, they don't have an incest taboo anyway, so it doesn't matter.
• The Casual Video Game Virtual Villagers allows you to control up to ninety individual village-members with their own names, appearance, and skills. The females can get knocked-up. By anybody. That includes their brothers, fathers, and offspring (assuming the offspring is old enough). Thankfully, the game doesn't actually keep track of family relations (which is probably why this is possible), sparing the sensibilities of players who forget or don't pay much attention to the lineage. Or turn their back on randy relations for half a second.
• Yumina the Ethereal has a Not Blood Siblings example. Yumina Midorishita is the biological daughter of Yumika Midorishita, while Ayumu Akashima is the adopted son of Takehito Akashima. Later on, it's revealed that Yumika and Takehito were High-School Sweethearts and that Takehito is also Yumina's biological father. In Yumina's route as well as the True ending, Yumina and Ayumu fall in love and hook up before the revelation that their parents are lovers, but even after they find out, they don't realize the implications that they're technically siblings until someone else points it out much later. Their immediate reaction is embarassment and disgust, followed by Ayumu trying to justify that it's okay because he's adopted while Yumina tells everyone (including Ayumu) to shut up because she doesn't want to think about how weird it is that her boyfriend is her brother, adopted or not. It doesn't help that Takehito fully acknowledges that they're both his children while still being extremely supportive of their relationship. Fortunately for them, the fact that they're siblings was never mentioned again after this scene.

Web Animation

• In the ACTUALLY HAPPENED video I Saw Something CREEPY In My Bf's Old Family Album, the twist is that the girl is dating a cousin she never knew about. She promptly breaks up with him, but never tells him that they're cousins.
• In the Dorkly Originals animation, "If video games were 69% more realistic", Diddy Kong realizes his last name is the same as Dixie's, Candy's, and Donkey Kong's, and he immediately questions if they are related, which is confirmed when all four of them say the name of their grandfather, Cranky Kong.
  Donkey Kong: Okay. So... Honestly, our history of incest explains a lot.

Web Comics

• A-gnosis' retelling of Classical Mythology has one-sided surprise incest between Zeus and his daughter Persephone. By the time Persephone realizes that Zeus pulled a Bed Trick on her, she's pregnant.
• In Arthur, King of Time and Space, Arthur sleeps with Morgan (in the space arc) and Morguase (in the baseline arc) without realizing the relationship. (Or vice versa — when Merlin finds out about Morgan he specifically notes that she should have been able to figure out who the mother of the rightful king must have been, but apparently she didn't. And Morguase didn't either, because if she had she'd have realized that her spell wouldn't work properly.)
  • In a Downplayed version, Gawain flirts with his sister Garet in the space arc, because she's disguised and he hasn't seen her in years.
• Played for laughs in Awkward Zombie in one comic, where Marth finds himself attracted to Lucina. When she reveals that she's his (very distant) descendant, Marth realizes that explained his attraction perfectly: Awkward Zombie's version of Marth is a narcissist.
• In Black Adventures, Black has a crush on his childhood friend White and is shocked to learn from Mom that she's his twin sister, who went with their father after the divorce. Mom is oblivious to Black's romantic intent and never got around to telling him that they're related until right before he was going to confess.
• In Chapter Twelve of Evon, Herodotus and Evon discover (to Evon's horror) that Corrin, the magic student she had a fling with in Chapter 4, is the half-sibling of Evon's they were hoping to find. It didn't help that Corrin got over his shock at warp speed and decided that silly little things like societal taboos don't apply to them because Screw the Rules, I Have Supernatural Powers!.
• Fate/type Redline: Kanata Akagi is a boy from 2020 who gets sent to 1945 and caught up in a Holy Grail War. He meets a girl named Tsukumo Fujimiya and they blush around each other, until he realizes she is the younger version of his grandmother.
• Happens in Hiimdaisy's parody of Apollo Justice: Ace Attorney, where it is revealed that the eponymous lawyer and his assistant and Phoenix's adoptive daughter Trucy are half-siblings from their mother's side. The game keeps mum about this and so do the two following entries although the latter does include a stinger where Phoenix tells their mother that it's time for Apollo and Trucy to know the truth. Time will tell if they did address it or not. Of course, the comic follows a path where they never found out, thus leading to this trope.
• Homestuck:
  • Happens twice to Dave Strider. He used to hit on Rose (ironically) before learning that they were brother and sister. In Act 6, he and Rose see their alternate universe mother in a dream, resulting in the following conversation later:
    ROSE: You're wondering why I didn't tell you?
    DAVE: no
    ROSE: You're specifically wondering why I wasn't forthcoming with an answer to your question at the time, "hey who was that choice babe in the pajamas?"
    DAVE: god fucking dammit
  • Dave is an absolute Freudian field trip. It can be seen several times that he has an awkward attraction to the other members of his ectobiological family.
    TT: We've already established that all of your dreams are packed with enough homoerotic symbolism to lift Freudian theory from the ashes of discreditation.
• In Shortpacked!, Amber learns that her Abhorrent Admirer, the incredibly perverted Faz, is actually her half-brother due to her father's adultery. She's legitimately worried that he'll still hit on her after finding out, though, and puts off telling him until their dad's death forces the issue. Faz does lose interest in Amber, but even then it seems to be more a combination of a.) feeling betrayed that Amber didn't tell him sooner and b.) having found an actual girlfriend (who is also super pervy and probably would've been fine with an incestuous threesome).
• Inverted in Something*Positive: Vanessa slept with a guy called Brad (she was trying to figure out if she was in fact a lesbian) but it went no further, and later their parents were due to be married. Unfortunately, Brad choosing that moment to joke about the prior relationship caused Vanessa's mother to disown her, and later Brad's father dumped her, citing her treatment of her daughter.

Web Videos

• In Comix From The Underground, the Comix Scrutinizer reads Kit n Kay Boodle and is surprised to learn that the main characters, who constantly have sex throughout the comic, are not married, but have the same last name. Even after joking that the characters might be brother and sister.
• In the first campaign of Critical Role, Scanlan meets an attractive gnome musician who is working with some old friends of his, and the two flirt, compete and generally hit it off. Later, the friends have come back to stay the night with Vox Machina and the two gnomes head up to Scanlan's room...where Kaylie reveals that she is Scanlan's daughter from a brief relationship he had years ago, and she's come to kill him in revenge for leaving her pregnant mother. Scanlan is horrified and remorseful.
• Gayle: At least a couple times, Gayle is deluded enough (through constantly talking about Greek yogurt the first time, and heatstroke the second) that she hallucinates that her daughter Terry is Gayle's celeb crush Yanni, and starts 'getting flirty' with Terry. Terry is...unamused both times. (Made funnier by the Cast Incest subtext: Chris Fleming, who plays Gayle, is dating Melissa Strype, who plays Terry.)
  Terry: Christ, she thinks I'm Yanni again.
• The original plot of The Nostalgia Chick's "Thanks for the Feedback" would have been a parody of Luke and Leia, with she and The Nostalgia Critic finding out they were related after having sex.
• Real-Time Fandub:
  • In the Sonic Adventure 2 dub, one Running Gag was Shadow the Hedgehog fucking (and pissing on to mark his ownership) Eggman's wife Martha. Then in Sonic the Hedgehog (2006), Eggman calls Shadow his "greatest creation". Or in other words, Shadow the Hedgehog is a bitch-ass motherfucker.
  Shadow: Well, if you're my dad, that makes the last dub horrifying. God...
  • After a brief Hope Spot when Peter returns with the anti-table serum, Aunt May ultimately dies when the embarassment of finding out Spider-Man is her nephew right after flirting with Spidey drives her to will herself to death.
  May: Well this got weird real quick! Sorry about your whole shit! Listen. Listen! You better go, 'cause this got really weird, and I'm gonna die. I'm goin' to the fuckin' car with Tobey Maguire...
  Peter: I know, it's so weird! I don't want you to die, Aunt May!
  May: I'm goin' to Tobey Maguire Land, and it's the [deathly cough]

Western Animation

• The Amazing World of Gumball: In "The Slide", Mrs. Robinson is mentioned to have always told Rocky he had a face "only a mother could love." Seconds after being told such, Gumball realizes she unknowingly sent a date request to her own son, which Gumball rejects and covers up.
• Used in every Seth MacFarlane show.
  • Family Guy:
    • Happens in a Halloween episode. Meg and her friends actually get invited to a costume party, and she goes dressed as a Slutty Cat, complete with a mask covering 75% of her face. One game of spin the bottle/seven minutes of heaven later, she's escorted to the closet with someone in an all-concealing Optimus Prime costume. When they're in there too long, the door is opened to reveal it being Chris... While they're half-naked on the ground making out. They didn't take it well, and lines like "We did so much!" imply there was more than just lips involved, though they seemed to have gotten over it by the end of the episode, apparently realizing that (given who they are) they were lucky to hook up with anyone at all that night.
    • In "Valentine's Day in Quahog", Stewie decides to go back in time to the 60s to see what love was like. During the trip, he falls for a girl and kisses her, only to find out it is really Lois after she is picked up by Carl Pewterschmidt. Stewie ends up vomiting all the way back to the present.
  • American Dad!
    • A version of this played out in an episode where Roger painted a nude portrait of Hayley for an art class, then rented it out to Steve as masturbation material^note he didn't know it was her because the painting stopped at her lips. Hayley is naturally Squicked and tries to put a stop to it; at the end of the episode, Roger drops the bomb, which horrifies poor Steve (rather than blaming him, Hayley is sympathetic and just gets angrier at Roger for manipulating him).
    • In another episode Roger plays a prank where he makes Steve believe that Francine and Stan aren't his real parents. Under his false impression, he suddenly kisses a horrified Hayley, to Roger's delight.
  • On The Cleveland Show, Roberta wears a fat suit using a fake name to see if she can get by without her looks, and sure enough, the only person who treats her kindly is her stepbrother, Junior. Unfortunately, he soon develops a crush on her, and she has to pretend to move away to avoid breaking his heart or revealing the truth.
• Central Park: In Season 3 "Slumber-Dog-Molly-An-Aire", Shauna gets a text message from Marcus saying he'll be in Central Park with a friend from a different school and Shauna wants Molly and Hazel to come with her so she her future boyfriend. When Molly, Hazel, and Shauna finally meet Marcus and his friend, Shauna is disappointed to learn that Marcus' friend is her cousin, Bobby. Everyone is squicked out with the revelation.
  Shauna: (disappointed) Hey, Bobby.
  Bobby: Oh. What's up, Shauna?
  Molly: Wait. You guys know each other?
  Shauna & Bobby: We're cousins.
  Marcus: Whoa.
  Molly: Ew.
  Hazel: Nope. Don't do that.
• The episode "Roswell that Ends Well" in Futurama. While stuck in 1947, Fry accidentally gets his grandfather killed and figures that since he still exists, the attractive woman he thought was his grandmother couldn't possibly be. After he does "the nasty in the past-y", Professor Farnsworth explains to Fry that not only is she his grandmother after all, Fry's grandfather is Fry himself. By extension this makes Fry's parents' marriage incestuous due to the same Stable Time Loop, but neither could possibly know about that.
• In G.I. Joe: A Real American Hero, Lady Jaye once infiltrated Cobra by impersonating the Baroness. At one point, she kisses Baroness' boyfriend Destro. A later episode revealed Lady Jaye and Destro share common ancestors.
• The Legend of Vox Machina: Scanlan, a Horny Bard who flirts and sleeps with anyone who will have him, meets an abrasive gnomish woman named Kaylie during Vox Machina's attack on the Herd of Storms in Westruun. During the celebrations afterwards, Scanlan invites Kaylie up to his room, and she accepts. Once in the room, she ties him to the bed under the pretense of BDSM, before putting a dagger to his throat and telling him she's his daughter, here to kill him for abandoning her mother after a one-night stand. Scanlan is mortified, both because he forgot Kaylie's mother even existed, and for nearly sleeping with his own daughter without knowing it.
• Subverted in King of the Hill:
  • Joseph is getting closer to a girl who is actually his half-sister (since he remains ignorant about John Redcorn being his biological father). Peggy invokes Friend Versus Lover with Bobby, making sure he's always hanging around them so that they can't actually do anything together.
  • Also subverted in another episode: Bill goes back to his family's home and meets three women who want to jump his bones. The catch is that one is his blood cousin while the others are the widows of his male cousins, and he doesn't know which is which. By the end of the episode, he figures it out and manages to sleep with both of the others.
• Mike Tyson Mysteries
  • One episode involves a couple who doesn't want their daughter to marry a man. As it turns out, the man is the husband's son from an affair with a pig. They end up marrying despite being related (and the fact the man is half-pig). Mike and his friends are grossed out by it all.
  • The episode "Your Old Man" reveals that Yung Hee's biological father is none other than Pigeon (though only Pigeon himself finds out about this), who has hit on her numerous times, and Yung herself expressed attraction to Pigeon after seeing what he looked like as a human.
• An episode of The Simpsons has Mayor Quimby telling his date at a wedding to say she's his niece if anyone asks. She responds "I am your niece, Uncle Joe!", and Quimby mutters "Dear God, I'm an abomination!"
• Played for laughs in Teenage Mutant Ninja Turtles (1987). Krang is shown to be watching a soap opera, featuring two characters in a passionate love affair. Marcia reluctantly explains to John that they can't marry because she's his twin sister, from whom he was Separated at Birth during a hospital blackout. John assures her that it's all right because he's not her brother - when he was born, an insane nurse switched him with another baby. Krang is openly weeping.
  Krang: It's so *sob* true to life!
• A technical version appears in Teenage Mutant Ninja Turtles (2012). Leonardo and Karai have a very Dating Catwoman relationship. It's later revealed that Karai is Splinter's daughter, making her and Leo Not Blood Siblings.

Real Life

• There was an incident in Virginia where a doctor (secretly) used his own sperm for all his artificial inseminations, meaning that a community now has many couples who might well be half-siblings. More of such cases of fertility fraud have been discovered over the years, including one confirmed case where a woman discussing her own discovery of her actual paternity at her high school reunion led her former boyfriend to investigate his own donor paternity, with the revelation that they were indeed half-siblings. Another woman with several donor half-siblings chose to pursue Age-Gap Romance in order to avert this possibility.
• A Minnesota school hosts a pep assembly. Part of it is having various athletes receiving blindfolded special kisses from a secret admirer... their parents.
  • This is a classic pep rally "gag" of long tradition, though normally it is much more innocent. Blindfolded football players are told they must guess which cheerleader kissed them (usually just a chaste peck on the cheek)... lift blindfold — surprise! It was actually Mom — ha-ha. (Embarrassment and teasing ensue.) However, in the incident referenced above, parents were practically making out with their kids.
• Happened to no less than Giacomo Casanova. According to his autobiography, he was on the verge of marrying a beautiful seventeen-year-old girl when he recognized the girl's mother as a former lover... from seventeen years earlier. She confirmed the girl was his. In real life he broke off the engagement immediately; in his liberally fictionalized autobiography, however, he cheerfully admits to an incestuous threesome, and even impregnated the daughter with their son/grandson years later when they meet again.
• Chevalier de Villiers entered high society under the tutelage of French philosopher and patron of the arts Anne "Ninon" de l'Enclos. Ninon, a (former) courtesan and beauty, had drawn the hearts of men to her throughout her life, and the heart of the Chevalier was no exception. He proclaimed his love and passion for her, only to be sent away. After begging for the privilege of seeing her again, he violated the condition of truce and declared his love once more. Using the reason of age, Ninon claimed that it would be unbecoming of her sixty-five years (to his 20s) to love and be loved. The Chevalier wouldn't take "no" for an answer, and Ninon withdrew even her friendship from him. Upon discovery that the Chevalier had fallen into despair and fury on account of her rejection, she elected to see him to tell him the Awful Truth: "The lover you are pursuing is your mother." Ninon burst into tears and held her son to her heart, and the Chevalier — who could not bring himself to utter the name 'mother' to the one whom he felt such a burning passion for — trembled, stared longingly into her eyes, and fled into the garden with a deep sigh. Ninon followed, and beneath the starry sky, the image before her was that of her son weltering in his own blood, shed by his own hand for his love for her. His dying eyes turned toward her and still shone of ardent love for her, and he passed while still uttering words of endearment.
  Ninon: It is my son who sighs at my feet, who talks to me of love.
• There was a case in the UK where twins who were separated at birth got married without realizing they were related. They had the marriage annulled after they discovered the truth.
• Somewhere in Britain there allegedly is a gravestone raised in the late 17th century to a woman who was the buyer's "mother, sister, mistress and wife". Apparently the deceased was impregnated as a young woman by her own father; the baby boy was sent to another village and came back a man, started an affair with an older woman he met there and later married her, and only then did she recognise a birthmark on his body...
• In 2013, Icelandic biotechnology company deCODE genetics held a competition among Icelandic students to develop mobile apps which utilize the data collected in "Ìslendingabók", a genealogical database built and maintained by deCODE. The winning entry was ÍslendingaApp, which, alongside various other services, allows two Icelanders who both have the app to instantly check whether, respectively in what way, they are related. The app can also be customized to give a warning called the "incest spoiler" if the two users share at least one grandparent. Though this optional feature was used to advertize ÍslendingaApp as a safeguard against accidental incest, incest prevention was never the app's primary purpose, and the "incest warning" was, at least partially, included for joke's sake. Contrary to what has been reported internationally, accidental incest is not a bigger problem in Iceland than anywhere else in the world.
• One of the concerns with donor children not knowing who their parents are, is the potential for this issue. It’s actually more likely to happen than people realize, possibly related to the known phenomenon of people marrying those who smell like their biological parents.

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