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[[quoteright:350:[[Webcomic/{{Hiimdaisy}} http://static.tvtropes.org/pmwiki/pub/images/surprise_your_siblings_1077.jpg]]]]
[[caption-width-right:350:[[Franchise/AceAttorney Phoenix Wright]] [[SuperDickery Is A Dick]]]]

->''"How was I supposed to know that we were both related?\\
Believe me, if I knew she was my cousin we never woulda dated."''
-->-- '''Music/WeirdAlYankovic''', "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 ArrangedMarriage 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 BrotherSisterIncest 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 [[NotBloodSiblings the genetics aren't a problem after all]].

These days, many people are {{squick}}ed 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 several kids with her before things fell apart (to the extent that TheReveal resulted in Oedipus's mother killing herself and Oedipus himself stabbing his own eyes out), so this is OlderThanFeudalism. 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, half-siblings, parent/child (much rarer these days than it was in ancient Greece), or, very rarely, uncle/niece or aunt/nephew. [[KissingCousins Cousins]] are only borderline {{squick}}y since marriage between cousins is actually legal in most places, and is quite acceptable in many romance novels. In fact, in the ''Literature/ArabianNights'', a man will call a woman he loves or is married to "daughter of my uncle", because in 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.

The relationship is more like to be on the paternal side, because of MamasBabyPapasMaybe. Historically was a fairly common way of making the Veronica of a BettyAndVeronica off-limits.

If the characters don't know the truth in advance but the audience does, this overlaps with DramaticIrony.

'''Expect spoilers.'''



[[folder:Anime & Manga]]
* ''Anime/PleaseTwins'' 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 main 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.
* ''Manga/MayasFuneralProcession'' has the main character, Reina, falling in love with [[spoiler:a mysterious girl named Maya]], only to discover that [[spoiler:Reina is the product of her mother's affair with Maya's father]] and thus they're actually half-siblings.
* ''Manga/KoiKaze'' has 27-year-old Koshiro and 15-year-old Nanoka having a [[MeetCute 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 BrotherSisterIncest, 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.
* ''Franchise/{{Gundam}}'':
** Depending on your interpretation of their relationship before the big reveal, Kira and Cagalli of ''Anime/MobileSuitGundamSEED''. 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 ''Anime/MobileSuitGundam'', with Kira and Cagalli having roles roughly analogous to Amuro and Sayla. WordOfGod is that this was a deliberate reference to Luke and Leia.
** Speaking of Sayla, in the ''Manga/MobileSuitGundamTheOrigin'' version of her first meeting with Char (who is suffering a serious case of AdaptationalVillainy) [[AttemptedRape he tries to rape her]] before [[OhCrap recognizing who she is]].
* Negi and [[spoiler:Asuna]], one of the most popular and [[ShipTease teased]] pairings in ''Manga/MahouSenseiNegima'', [[spoiler: are ''very'' distantly related by the Lifemaker, maybe closer, but how close was never specified]].
* In ''Manga/CountCain'', 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 other brother/sister couples as throwaway characters, too.
* Averted in ''LightNovel/{{Slayers}}'': Thankfully, Zelgadis stating that Rezo was both his grandfather and great-grandfather turned out to be a translation error.'
* Falan and [[spoiler:Ilsaid]]'s dad in ''Manga/VampireGame'' did not inform them that they were related, until his son asked for his sister's hand, that is. He then only told his [[TheUnFavourite Unfavorite]], though.
* ''Manga/DetectiveConan'' has a case [[spoiler:with Raita Banba and his fiancee, Hatsune Kamon]]. Uniquely, it turns out that [[spoiler: they're twins and that the latter has [[http://en.wikipedia.org/wiki/Turner_syndrome Turner syndrome]] ]]. [[spoiler: 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. [[spoiler:When she gets the test results confirming it, she... [[DrivenToSuicide doesn't take it well]]. And for worse, ''[[CrazyJealousGuy Raita]] is accused of having killed her in a {{Yandere}} fit''. Conan, through Kogoro, has to clear his name.]]
* ''Manga/VampireKnight'': When Kaname turns Yuuki into a vampire, restoring her memory, she reveals to the audience that Kaname is her brother. Ah, so the LoveTriangle 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 -- [[DeliberateValuesDissonance this is very common among pureblood vampires]], and in fact their own parents (Juri and Haruka) were siblings and HappilyMarried. [[spoiler: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 [[DoubleSubversion double subverted]].]] The situation is exactly as complicated as it sounds.
* The prince and princess from ''AndromedaStories'', a pair of HalfIdenticalTwins who were SeparatedAtBirth, 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.
* Kanba and Masako subvert this in ''Anime/MawaruPenguindrum''. They know about their bond and have it more or less clear (though Masako has quite the case of BigBrotherAttraction as shown when she ''kisses'' Kanba), but it's a surprise to the ''audience'' and to Kanba's adoptive sister Himari. Doubles as {{Twincest}}.
* In ''Manga/DailyLivesOfHighSchoolBoys'', Emi, after days of CannotSpitItOut, 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."
* A possible example is [[spoiler: Millernium "Milly" Feria Noctum and Kane Blueriver]] in ''Anime/LostUniverse'', 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 [[spoiler: Kane survives the end of the series]] anyway.
* In Part 6 of ''Manga/JoJosBizarreAdventure'', a [[SwitchedAtBirth baby switch]] eventually led to Pearla Pucci dating her older brother, Wes ([[spoiler:aka 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...
* In ''Manga/{{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.
* ''Anime/DragonBallZ'' has a minor example with Bulma gently hitting on Trunks well before she learns that he's her KidFromTheFuture.
* In ''Anime/JewelpetSunshine'', 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.
* In one of the ''Manga/TheLegendOfZeldaI'' manga, an adaptation of ''VideoGame/TheLegendOfZeldaI'', 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 relatively, and doesn't requite Link's feelings, but is never shown telling him that they're related.
* While the characters never know it, ''Anime/BirdyTheMighty Decode'' sees this: [[spoiler: Nataru, the titular Birdy's love interest and childhood friend was, like her, created in lab as a SuperSoldier--the same lab to be precise, which means there's a good chance Nataru and Birdy are brother and sister]].
* In the first chapter of ''Manga/FamilyCompo'' 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 KissingCousins, with a lean towards the latter.

[[folder:Comic Books]]
* [[spoiler:Jack]] from ''Jack of Comicbook/{{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 [[{{Pun}} relatively]] well, his sisters, [[BrainBleach not so much]].
* ''ComicBook/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. And 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 2nd 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...
* In Comicbook/{{Supergirl}} storyline ''Comicbook/ManyHappyReturns'', Kara Zor-El -the original Supergirl- and Kon-El -Comicbook/{{Superboy}}- meet and find each other cute (Kara is visibly smitten with him). Neither of them knows at the beginning that Kara is cousin of Kon's genetic template.
* A story arc in ''ComicBook/TheFabulousFurryFreakBrothers'' 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!"
* ''Magazine/{{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. [[ShaggyDogStory The love affair ends before it starts]].
** In the parody of ''Maverick'', the [[WhamLine final line]].
-->"There's still one final plot twist--you can't marry your own sister!
* ''ComicBook/{{Shazam}}: The Monster Society of Evil'' has a thankfully low-key example: Mary seems to have a PrecociousCrush on the superhero who just [[RescueRomance 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 OlderAlterEgo of her [[LongLostRelative 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.
* In an issue of Jason Aaron's ''Comicbook/{{Thor}}'' 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 a beautiful young Goddess named Ellisiv, who turns out to be one of his descendants from the far future.
-->'''Ellisiv''': Thor? Oh my Heavens...I've been having impure thoughts about my ''grandfather''.
* ''ComicBook/{{Blacksad}}'': [[spoiler:Hans Karup]] unknowingly married one of his own daughters after she came of age. She was actually aware of their family relationship, and [[LysistrataGambit 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.

[[folder:Fan Works]]
* ''Fanfic/HigherLearning'': While [[spoiler:Shinji was stuck into the Twelfth Angel]] Asuka [[spoiler: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 [[spoiler:Kaoru confessed that he was her GRANDSON.]]
* In ''[[http://percyjacksonfanfiction.wikia.com/wiki/Love_Kills Love Kills]]'', a ''Literature/PercyJacksonAndTheOlympians'' fanfiction, [[spoiler: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.
* The doujinshi ''VideoGame/GoldenSun 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.
** Not to mention the fandom's unofficial name for the Felix/Jenna pairing is "[[LampshadeHanging Oopsie-shipping]]".
* In ''FanFic/TheDarknessSeries'', a Voldemort/Harry fic, Harry learns he's related to Voldemort on both sides of the family tree. [[VillainousIncest They don't think too hard about it.]]
* In ''[[FanFic/EakinsHardReset Hard Reset]]'', Twilight figures she might as well use a GroundhogDayLoop 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. [[spoiler:Celestia then reminds Twilight that 1,600 years is probably sufficient time. 'Youíre probably more closely related to a random unicorn wandering the streets of Canterlot, genetically speaking.']]
* Played straight in the ''WesternAmination/AvatarTheLastAirbender'' fanfic ''Embers'' where it is revealed that the relationship between [[spoiler: Zuko and Mai]] was a secret case of [[KissingCousins kissing cousins]] orchestrated by [[spoiler: Azula]] in order to have leverage on them.
* In ''VisualNovel/ApolloJusticeAceAttorney'', we see the protagonist, Apollo Justice. His attractive assistant is Trucy Wright, Phoenix Wright's daughter. They got a bunch of ShipTease 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, [[DramaticIrony they themselves never do]] (although at the end of ''VisualNovel/PhoenixWrightAceAttorneySpiritOfJustice'', Phoenix and Thalassa decide it's time for them to know).
** Parodied in [[http://i.imgur.com/4g8zuku.png this fancomic]] by ''Webcomic/{{Hiimdaisy}}'', which also provides the page image.
* Played for tragedy in the ''Franchise/StarWars'' fanfic ''[[https://www.fanfiction.net/s/2080032/1/The-Shadows-Suit-Me The Shadows Suit Me]]'' between Luke and Leia.
* The ''Disney/{{Frozen}}'' fanfic ''Fanfic/StolenIce'' has this occuring 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.
* Due to the growing relationship between [[{{Polyamory}} Asuka, Rei and Shinji]] in Fanfic/NeonMetathesisEvangelion, Rei and Shinji are headed that way.
* ''Fanfic/FatesCollide'': 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.

* ''Franchise/StarWars''. Yes, ''Star Wars''. Media such as ComicBook/MarvelStarWars and Literature/SplinterOfTheMindsEye, produced before Lucas decided Luke and Leia were twins, makes it explicit that they're mutually very interested, but in ''Splinter'' neither of them is aware that the other feels the same, and in ComicBook/MarvelStarWars being interrupted every time their relationship goes beyond declarations of friendship and [[HoldingHands hand-holding]] is a RunningGag. Said gag might have been a continuation of [[http://www.starwarsholidayspecial.com/swcs/episode5/mask.html a scene]] cut from ''Film/TheEmpireStrikesBack''. At one point, Leia kisses Luke, but the movie makes it clear she did it just to spite Han.
* ''Film/FuneralParadeOfRoses'': 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 GenderFlip update of ''Theatre/OedipusTheKing''.
* In ''Film/AFunnyThingHappenedOnTheWayToTheForum'', the heroine is a virgin slavegirl arranged to be sold/married off to the Roman general responsible for having destroyed the land where she grew up. She is somewhat reluctant to marry even before she falls in True Love with the hero. But everything ends happily when a set of matching rings proves the general and his prospective bride are long-lost siblings, enabling the hero and heroine to marry.
* Inverted in ''[[Film/CaveDwellers 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.
* Parodied in ''Film/BackToTheFuture'' 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 [[GutFeeling women's intuition]], [[RubberBandHistory the timeline trying to correct itself]], or just [[MaybeMagicMaybeMundane finally cottoning on to Marty's obvious discomfort]].
* ''Film/MyChauffeur'' flirted with this. As one of several [[TheUnreveal seeming reveals]] about who the female lead's "real father" was. Apparently Mom got around.
* ''Film/{{Oldboy 2003}}'', in which the main character is the victim of an elaborate revenge/imprisonment plot, [[spoiler: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]].
* This is the whole plot behind ''Film/SayItIsntSo''. Faux-Farrely hijinks ensue.
* The major couple in ''Film/TheBeastmaster'' 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 [[NotBloodSiblings not blood cousins]] after all. She could always be the niece of the king's second wife.
* The Japanese film ''Film/BubbleHeNoGo'' 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.
* Parodied in ''Film/JoeDirt''--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 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."
* Becomes a main plot arc in ''Film/{{Incendies}}'' when [[spoiler: 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]]!!!
* ''Film/{{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; [[spoiler: 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]].
* Played for laughs in ''Film/DirtyWork'': 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 FridgeHorror hits them both] Okay, enough reminiscing.
* In ''Film/LoneStar'' [[spoiler:two characters that had dated in high school over their parents' STRONG objections reconnect as adults. 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. 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]].
* In ''Film/TromeoAndJuliet'', 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.
* Kind of inverted in ''Disney/MeetTheRobinsons''. Louis 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 [[spoiler: she is actually his future wife]]. One wonders how he wasn't the least bit {{squick}}ed out when [[spoiler: he meets her for the "first time" in the past]].
* In the film ''[[Film/ManonDesSources Jean de Florette]]'' Papet and his nephew Ugolin drive a hunchback to his death in order to get his land. In the sequel ''Manon of the Spring'', [[spoiler:Ugolin sees the hunchback's daughter Manon 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]].
* In the Michael J. Fox film, ''Film/TheSecretOfMySuccess,'' 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 [[TwoPersonPoolParty 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 ''Film/CurseOfTheGoldenFlower'', [[spoiler:Chan and Wan]] eventually find out they're half siblings, and take it [[FreakOut about as well as you'd expect]].
* In Japanese film ''Film/{{Inugami}}'', [[spoiler:Miki and Akira]] discover that they are mother and son. They also discover that [[spoiler:Akira]] is a product of [[BrotherSisterIncest another, similarly themed trope]].
* Invoked in the Spanish film ''Km. 0'' - a woman hires a gigolo for an extra-marital fling, then comes to believe he's the son she gave up for adoption years earlier. [[spoiler: The actual son turns out to be the gigolo's roommate, to her great relief.]]
* In ''Film/{{Zathura}}'', Lisa immediately starts harboring a crush on the astronaut once she awakens after having been [[HumanPopsicle being frozen]] for most of the movie. He tries to brush off her advances, presumably because she's jailbait. Later in the film [[spoiler: 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.)
* In the film ''Film/AnAwfullyBigAdventure'', P. L. O'Hara, an aging actor, seduces a teenage girl, only to find out later that she's his daughter. [[spoiler:The distraction caused by this discovery leads to his death.]]
* In ''Film/AngelHeart'', 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 [[TomatoInTheMirror he himself is Johnny later on]]. To make matters worse, [[spoiler:he later killed her while under Satan's influence.]]
* In ''Film/WarInc'', Yonica keeps hitting on Hauser, which creeps him out because she's a teen and he's an adult. [[spoiler: At the end, they find out they're father and daughter.]]
* In ''Film/{{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 when she didn't know 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 extended cut of ''Film/WildThings'', Suzie is revealed to be Kelly Van Ryan's aunt. 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. It's subverted in that no one except Suzie was ever aware of this and Kelly never learns the truth.
* In ''Film/TheJudge'', 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! [[spoiler:It turns out she's his niece, as the disgruntled ex slept with Hank's brother.]]
* The 1920 silent film ''Film/WithinOurGates'' 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.
* ''Three seats for the 26'', 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 attacked 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 TheReveal. Montand however '''is''' pretty horrified but after seeing Marion's nonchalant attitude towards the whole mess, he relaxes and realizes that perhaps ParentalIncest isn't such a horrid taboo, all things considered. They all become a happy family.

* In Frances Burney's 1778 novel ''Literature/{{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.
* 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.
* 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 ''Literature/TheHistoryOfTomJonesAFoundling'', a random one night stand is later seemingly revealed to be the protagonist's mother... Oh NO! Our hero has done something legitimately bad! [[spoiler: Fortunately, this is later resolved to be a lie.]]
* ''Discworld/{{Pyramids}}'' by Creator/TerryPratchett features a pair of romantically inclined half-siblings who eventually figure it out (before getting seriously involved). This one might be a ShoutOut to ''Franchise/StarWars'', as the non-related male love interest is a LovableRogue smuggler with a CoolShip. (Also there's a bit of a twist, what with them being royalty in [[FantasyCounterpartCulture 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.)
* In Creator/OrsonScottCard's ''Literature/SpeakerForTheDead'', 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.
* In the Peter David novel ''Literature/SirAproposOfNothing'', 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. [[spoiler: 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.]]
* Creator/JRRTolkien's ''Literature/TheSilmarillion'' includes the tale of Túrin Turambar (dealt with at greater length in ''Literature/TheChildrenOfHurin''), 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 a dragon. Therefore, not knowing who she is, they get married and she even gets pregnant, but then the dragon restores her memory and she promptly commits suicide. Túrin does the same shortly afterwards. [[WholePlotReference Based on the story]] of Kullervo in ''Literature/TheKalevala''.
* In ''Literature/OneHundredYearsOfSolitude'', 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, [[spoiler: aunt and nephew respectively,]] mate and give birth to a pig-tailed baby [[spoiler: 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, [[spoiler:just seconds before the destruction of the town]].
* In Poppy Z. Brite's novel, ''Lost Souls'', a teenage runaway called Nothing meets up with a trio of real vampires led by the captivating Zillah, and becomes Zillah's lover. Halfway through the novel, it's revealed that [[spoiler: Zillah is Nothing's father]].
* In ''Literature/ThievesWorld'' 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 AxCrazy, though in different ways. Some early stories danced around whether they really were related, but Janet Morris' ''A Man and His God'' confirmed 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 [[spoiler: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, [[spoiler:long after Penelope has died giving birth to Julian's child]], that he learns that she was actually his half-sister.
* In the novel ''Literature/MollFlanders'' 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.
* ''Literature/ASongOfIceAndFire'':
** Theon Greyjoy's [[SheIsAllGrownUp unrecognized]] tomboy sister practically seduces him until TheReveal to purposefully mess with his head, and see what kind of man he's grown into during their separation.
** Almost used later when Gendry, [[DisappearedDad 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 ([[IfOnlyYouKnew 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 Creator/RobertAHeinlein's ''Literature/{{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 Juliet Marillier's novel ''Literature/SonOfTheShadows'', 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 because [[spoiler: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 [[spoiler:daughter]] turns out to be [[spoiler: the child of the prophecy, ending a longstanding feud with Britain over sacred ground]]. Unfortunately, [[spoiler: 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 [[spoiler:Bran/The Chief]] are second cousins.
* In ''Literature/{{Lirael}}'' by Creator/GarthNix, Prince Sameth shows some interest in Lirael, without knowing [[spoiler: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 [[spoiler: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 ''Literature/KafkaOnTheShore'' 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.
* In ''[[Literature/TheMerlinTrilogy The Hollow Hills]]'', the second book in Mary Stewart's retelling of the story of KingArthur, Morgause, Arthur's half-sister, bewitches him into sleeping with her, and he only finds out afterward of their relation to one another.
* Subverted in ''Literature/TheElvenbane'' by Creator/AndreNorton 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 IdiotBall when he refuses to tell her why he is rejecting her even though she is hurt and angry about it. His excuse? She was RaisedByWolves (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.
* In the first trilogy of ''The Chronicles of Thomas Covenant'' Thomas [[spoiler: 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 the Creator/JinYong novel ''Demi-Gods and Semi-Devils'', all the women Prince Duan Yu has relationship 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 ''Franchise/{{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.
* Lydiann Ebersol and Jake Mast fall in love and agree to marry in ''The Prodigal'', the 4th book of the [[Literature/AbramsDaughters Abram's Daughters]] series. Unbeknownst to them, Jake is Lydiannís blood nephew Ė- being the biological son of Lydiannís (unwed) sister Sadie, who was then adopted by the Masts.
* The incest is averted in ''Literature/{{Havemercy}}'', but just barely. WordOfGod 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 ''Literature/TheMistsOfAvalon'', a [[FeministFantasy feminist retelling of Arthurian legend]], [[TheChessmaster 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.
* Happens not once, but ''twice'' in ''Literature/TheStoneDanceOfTheChameleon''. Carnelian and Osidian meet in secret and have a passionate affair. Then it turns out that [[spoiler:Osidian is the GodEmperor's son, making them [[KissingCousins cousins]], since Carnelian's mother is the emperor's sister. Later, though, it turns out that Carnelian's father is actually [[BrotherSisterIncest the emperor himself]] -- which is not atypical in the ruling house, Osidian's mother being the emperor's other sister. Making them, you know, [[SiblingIncest brothers]].]] In case you hadn't noticed, this is [[RoyallyScrewedUp one messed up family.]]
* In the crime novel ''Literature/LieToMe'' 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.
* Subverted in ''Literature/TheMortalInstruments''. Clary and Jace are revealed to be siblings at the end of ''City of Bones''. They spend all of ''City of Ashes'' and most of ''City of Glass'' angsting about their attraction, until it's revealed that [[spoiler:[[NotBloodSiblings Jace was adopted.]]]] Played straight with [[spoiler: Sebastian/Jonathan, Clary's ''actual'' brother, [[VillainousIncest who kisses her despite knowing full well that she's his sister.]]]]
* ''Literature/TheMonk'': As if raping [[TheIngenue Antonia]] wasn't enough, Ambrosio later learns she is his much younger sister.
* In the final Literature/{{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 ''Literature/SherlockInLove'', SherlockHolmes finds himself falling in love with the astoundingly intelligent and musically-gifted Violet Sigerson. [[spoiler: 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 [[FakingTheDead fakes her death]] to stop him forever.]]
* In ''Literature/ABrothersPrice'', Jerin and Ren hit it off to the point where he's left a TechnicalVirgin. Then they find out that because his grandmothers [[AbductionIsLove 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 [[KissingCousins it's fine]] and later others agree. Many of the nobility are somewhat more inbred than commoners, and actually this reveal makes him a SuddenlySuitableSuitor.
* Max Frischís ''Homo Faber''. The novel is mostly just the narrator whining that he really, ''really'' couldnít have known that the young woman he slept with was his daughter.
* 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 [[spoiler: had a child by her brother, killed that child in self defense when he was trying to take her sexually, and married her father.]]
* Severian of ''Literature/TheBookOfTheNewSun'' 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 [[spoiler: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.
* 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.
* 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 [[spoiler: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]].
* One of the three protagonists in the web serial ''Literature/{{Addergoole}}'' [[spoiler: Shahin]] has an intense romantic affair with another student [[spoiler: Emrys]]. Later, it turns out that they're half-siblings, sharing a father. [[spoiler: 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.
* Josephine Angelini's ''Starcrossed'' series plays with this trope twice:
** Helen is kidnapped by [[spoiler:her MissingMom]] who tells her that [[spoiler: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. . .[[spoiler:and her mom]]. Just as she starts freaking out, Orion quickly explains that it wasn't what it looked like and [[spoiler: Helen's mom helps his dad take care of Orion's mom sometimes.]]
* 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 [[ChildbyRape 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 [[DrivenToSuicide 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 ''Literature/TalesOfTheFiveHundredKingdoms'' series, the Tradition (a magic force that makes people's lives follow fairytale plots) will allow BrotherSisterIncest only if it's this. If the relatives knows each other, they won't be compelled to fall in love even if it suits another Traditional path (i.e. RescueRomance).
* In ''Hearts of Three'' by Creator/JackLondon 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 [[IGaveMyWord they were engaged before she met the other one]]. Practically at the last moment, her fiancé turns out to be her brother.

[[folder:Live Action TV]]
* An unusual example in ''Series/TrueBlood'', in which vampire Bill finds out his human squeeze Portia is actually his 3rd great-granddaughter, but Bill is the only one who's grossed out by this. Portia is more than willing to continue their relationship (and great sex), citing logical reasons why this shouldn't affect them (e.g. their genetic differences are about the same as with any other person, there's no risk of children since he's a vampire, most states are rethinking their cousin marrying laws). Bill then [[MoreThanMindControl glamors]] her into having a screaming fit every time she sees him. Maybe in addition to the incest he didn't want to be Sheriff Andy Bellefleur's brother-in-law.
* Happened in a 2007 plotline in the SoapOpera ''Series/{{Hollyoaks}}''.
** 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.
* Occurred in at least one plotline in ''Series/LawAndOrderSpecialVictimsUnit''. [[spoiler: 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, 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 [[spoiler: 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, 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.]]
* One episode of ''Series/{{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.
* Hispanic {{soap opera}}s 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 "''[[http://www.planetadeletras.com/index.php?m=s&lid=77646 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.
* ''Series/AsTheWorldTurns'': 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.
* ''Series/RedDwarf'':
** It was revealed that Lister's ex-girlfriend Kochanski is actually his mother. In the next series, Lister still uses a [[LovePotion 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 [[MyOwnGrampa 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 [[spoiler: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.
* In the 2007 remake of ''Series/{{Flash Gordon|2007}}'' [[spoiler:Aura and Terek]] were in place to start up a romantic relationship, only for Flash to burst into the room to inform them that they are siblings. Later, it turns out they're twins.
* ''Series/JustShootMe'':
** Jack's handsome new ex-marine trainer keeps trying to ask Nina out. Nina, who usually ReallyGetsAround, 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 an affair with this friend 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, however, Nina's broken the news to the would-be couple, and the man is horrified.
* In the ''Series/ThirtyRock'' 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:
-->'''The Hair''': I think we're third cousins.\\
'''Liz''': Yeah, I'll see you at the reunion.
* On ''Series/GroundedForLife'', Lily made out with a guy at the funeral. She later learns he was her cousin. Then she is somewhat relived when she learns he was a cousin by marriage but squicked again when learning they're cousins by his marriage.
* On ''Series/GreenWing'', Guy Secretan doesn't find out [[spoiler:Joanna]] is his long-lost and presumed-dead ''mother'' until after they've slept together. And it's been caught on tape.
* The Korean soap opera ''Series/WinterSonata'' is ''Series/MarmaladeBoy'' if Yuu went missing, got amnesia, and [[spoiler: 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!".
* In ''Series/VeronicaMars'', 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 PutOnABus).
* In the ''Series/{{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.
* ''Series/{{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.
* On ''Series/NipTuck'', the Carver and the female police officer investigating the case are siblings. Who are sleeping together. 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.
* ''Series/{{Carnivale}}'': All right, we'll be fair: [[spoiler: Justin Crowe]] wasn't actually ''aware'' that he'd made creepy passes at ''two'' close female relatives. After all, [[spoiler: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.
* On the British soap ''Series/{{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.
* On Creator/{{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).
* On ''Series/{{Smallville}}'', when Clark meets Kara (aka Comicbook/{{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 up, clearly (and understandably) disappointed.
* ''Franchise/KamenRider'':
** ''Series/KamenRiderDouble'' has a strange example that's not quite playing with and may be a RelationshipWritingFumble or may have been intentional. [[spoiler:Phillip]] is really the brother of [[spoiler: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 {{lampshad|eHanging}}ing. Although, to be fair, he never really seemed to think of her that way. [[{{asexuality}} Or any other girl or guy for that matter.]]
** ''Series/KamenRiderDenO'' likewise [[ShipSinking sank the ship]] of [[spoiler:Ryotaro/Hana]][[note]]which already took a massive hit when [[spoiler:Hana was [[FountainOfYouth de-aged to childhood]]]][[/note]] by revealing that the latter was the former's [[spoiler:Niece]] [[KidFromTheFuture from the Future]]. Thanks, TimeTravel! They still got off better than the [[spoiler:[[ParentalIncest Yuuto/Hana]]]] shippers, though.
** ''Series/KamenRiderKabuto'' has plenty of ShipTease for Tendou and Hiyori earlier in the series (with a guest actor who'd played Tendou as a child [[WordOfGod stating in an interview]] that he'd been led to believe Hiyori was Tendou's love interest.) However, Hiyori turns out to be [[spoiler: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.
* On ''Series/{{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.
* In a Season 5 episode of ''Series/TheATeam'', "Family Reunion," [[HandsomeLech 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 [[spoiler:this beautiful woman is actually his half-sister, and her fugitive father is also his]].
* In season 3 of ''Series/SonsOfAnarchy'' 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.
* ''Series/MidsomerMurders''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.
** In one, 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 BrotherSisterIncest.
* ''Series/{{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. [[spoiler: 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.]]
* [[spoiler: Zig-zagged]] on ''Series/ArrestedDevelopment''; Maeby has an on/off relationship with [[spoiler:Steve Holt]], who is ultimately revealed to be [[spoiler:her uncle GOB's illegitimate son (Played Straight)]]. This prompts the couple to break up, but it turns out that [[spoiler: 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.
* In one episode of ''Series/TheLoveBoat'', 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.
* In ''Series/TheNanny'', 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 {{Squick}}ed)''
* ''Series/BoredToDeath'': [[spoiler: Jonathon and his girlfriend find out they're half-siblings]]. Left unresolved due to cancellation.
* ''Series/BoyMeetsWorld'':
** In one episode, Eric hooks up with a girl at a [[ItMakesSenseInContext 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.
* A subtle one occurs in the relaunch of ''Series/{{Battlestar Galactica|2003}}'' where [[spoiler: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 [[spoiler:Ellen viewed Cavil as a son, he was also designed to look like her father. Just another sign of how deep his misanthropism and hatred toward his "parents" really ran]]. And while [[spoiler:Ellen was unaware of this due to amnesia, Cavil knew all about it and deliberately set it up.]]
* The end of the episode with the Pimp Hat in ''Series/LessThanPerfect'' had Owen and his DistaffCounterpart 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.
* This becomes a motive for murder on a case in ''Series/CSIMiami''. Dad had a SecretOtherFamily, son from Family A met up with daughter from Family B, fell in love, and had a baby together. Then son found out...
* In ''Series/{{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?
* In ''Series/{{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.
* In ''Series/{{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 test done. They find out not only that they are related, but they have 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.
* A common PlotTwist in soap operas is that some couple found out they are somehow related. Did I say common? ''Super common'' PlotTwist.
* ''Series/DaysOfOurLives'':
** The show had a scene in which [[spoiler: 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 [[spoiler: 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.
* ''Series/{{Arrow}}'': Early scenes suggesting a possible spark between [[spoiler: Tommy and Thea]] become squicky in hindsight after the Season 2 reveal that they [[spoiler: are half-siblings, sharing the same father. (Though Tommy was dead by the time it was revealed, making it a moot point anyway)]]
* In ''Series/LostGirl'', Bo gets hit on and kissed by a woman who turns out to be her long-lost mother (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 [[spoiler:Hades is her biological father, thus making Persephone her stepmother]].
* ''Series/HowIMetYourMother''
** 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 [[MatingDance 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 [[LetUsNeverSpeakOfThisAgain they must never speak of this again]], not even in the form of a [[NoodleIncident funny "Do you remember that time when..."-style anecdote]].
* ''Series/GameOfThrones'':
** 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 SecretTestOfCharacter. Needless to say, he failed miserably.
** As of Season 7, there is sexual tension developing between [[spoiler: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 [[spoiler:nephew and aunt; despite being the same age, as Jon is actually the son of Dany's much older brother Rhaegar]].
* ''Series/InspectorGeorgeGently'': "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.
* In ''Series/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.
* ''Series/TheGoldenGirls'' had an awkward relationship revealed at a wedding. Dorothy and a man were mutually flirting with each other and were thinking about dating. However, near the end of the episode, they both end up at a wedding of one of their relatives. Once there, Sophia casually mentions that the two of them are closely related cousins. They are both mutually creeped out.
* A ''Series/MadTV'' sketch parodying {{Korean Drama}}s ends with the main character and his love interest learning they share the same mother.
* ''Series/TheAffair'': Thankfully it doesn't get that far, but when Noah finds himself at APartyAlsoKnownAsAnOrgy thrown by a Hollywood producer, he checks out a TwoPersonPoolParty before realizing that one of the two kissing girls is his daughter Whitney. He quickly makes himself scarce.
* On ''Series/{{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".
** Later subverted when they realize Jace's lineage is not what he thinks and thus they're not related.
* In ''Series/MrRobot'', 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", [[spoiler: 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 ''Series/WaywardPines'', 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 [[spoiler: Kerry was unfrozen many years after Jason]].
* In ''Series/LegendsOfTomorrow'', 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).
* In the sixth season of ''Series/{{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. [[KissingCousins They decide to stay together anyway]].
* Defied in ''Series/NewAmsterdam''. The immortal protagonist John, who ''is'' very much capable of [[ImmortalProcreationClause 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.
* ''Series/{{Endeavour}}'': In "Trove", a man performing a DeadPersonImpersonation discovers he has just slept with his daughter. The girl had been an infant when he [[FakingTheDead 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.
* ''Series/FutureMan'': Josh almost has sex with his own ''mother'', having mistook her for someone else. He finds this out ''just'' in time before they get that far.

* 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 second verse of Music/WeirdAlYankovic's "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 "[[DeepSouth move to Alabama where that kind of thing is tolerated]]".
-->I was feelin' pretty down\\
'Til my girlfriend came around\\
[[FiveSecondForeshadowing 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
* 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.
* 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.
* ''[[http://sniff.numachi.com/pages/tiSHMSCNDL;ttSHMSCNDL.html Shame and Scandal]]'' subverts this: This young man discovers his dad is also the father of every single one of his girlfriends [[spoiler:then learns from his mother that his "dad" his not his real father]].
* The song "Butterflies" by Music/{{Sia}} 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".
* Cornelis Vreeswijk's ''[[http://www.youtube.com/watch?v=J_JJaay6i_c 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..."
* 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?
* The folk song "[[http://www.lyricsdownload.com/sainte-marie-buffy-johnny-be-fair-lyrics.html Johnny Be Fair]]" parodies this. The female narrator repeatedly falls in love with men, only for her father to pull out the ParentalMarriageVeto 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.
* 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."
* Music/TomLehrer 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'''''.
* Harry Chapin's "The Mayor of Candor Lied" is a particularly [[NightmareFuel 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...

* Oedipus' story in [[Myth/ClassicalMythology 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 [[DrivenToSuicide killed herself]] while Oedipus [[EyeScream put out his own eyes]]. Told famously in the tragedy ''Theatre/OedipusTheKing''. Despite the way this actually plays out, Oedipus somehow ended up as the {{Trope Namer|s}} for OedipusComplex even though he's not an example of that trope.
* 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 BoltOfDivineRetribution 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 version the trope averted wasn't SurpriseIncest but OffingTheOffspring - Auge still loved Heracles, so she brought a ChastityDagger along.
* Finnish mythology: Kullervo from ''Literature/TheKalevala'' 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.
* Myth/NorseMythology:
** In ''Literature/TheSagaOfHrolfKraki'', 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 [[ChildByRape conceived by rape]] on an earlier raid.
** In ''Literature/TheSagaOfTheVolsungs'', 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.

* In ''Theatre/TheMarriageOfFigaro'', 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.
* "[[http://en.wikipedia.org/wiki/Emmeline_(opera) 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.
* Itís 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 Leoö Janáčekís ''The Makropulos Affair'' itís revealed that all the time Albert Gregor has been vying for the love of his ''great-grandmother''.

* Shows up in the plays of Music/SamShepard from time to time as a {{deconstruction}} of UsefulNotes/TheAmericanDream.
* Used in ''Theatre/AFunnyThingHappenedOnTheWayToTheForum'' to get two characters out of an ArrangedMarriage and give the show a happy ending.
* 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 ''Theatre/NathanTheWise''--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 KnightTemplar 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.
* In ''Theatre/TheImportanceOfBeingEarnest'', it's revealed that Jack and Gwendolyn are long lost cousins, but they don't really care and still want to get married anyway, which was not unusual for the time and place.
* The story of Oedipus who unwittingly married his own mother is the subject of Creator/{{Sophocles}}' ''Theatre/OedipusTheKing''.
* Played with in ''The Guilty Mother'', the unpopular DownerEnding segment of the [[Theatre/TheBarberOfSeville Figaro]] [[Theatre/TheMarriageOfFigaro trilogy]]. Both lovers are not the biological offspring of both of their legal parents, and Figaro has to juggle their WhosYourDaddy plot so that they can marry and nobody needs to be publicly disgraced.
* 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.
* ''Theatre/AugustOsageCounty''. [[spoiler: Little Charles and Ivy have a KissingCousins relationship, which is made worse when it's revealed that Little Charles is actually the biological son of Ivy's father, making them brother and sister as well]].
* Subverted in the ''Theatre/ForbiddenBroadway'' parody of ''Theatre/SpringAwakening'':
-->'''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 Henrik Ibsen's ''{{Theatre/Ghosts}}'' [[spoiler: 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.

[[folder:Video Games]]
* In ''VideoGame/ShadowHearts: 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 [[spoiler: 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. [[spoiler: 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 become either [[FunnyAneurysmMoment squicky]] or more [[HilariousInHindsight hilarious]] afterwards depending on how perverted your sense of humor is]].
* In the ''Franchise/BaldursGate'' 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 [[GirlsLove 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 [[spoiler: you found out that Imoen was your half-sister]].
** This is actually brought up in ''VideoGame/BaldursGateIIThroneOfBhaal'', 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 {{squick}}ed 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 tried to do 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 the ''Franchise/FireEmblem'' franchise:
** In ''VideoGame/FireEmblemGenealogyOfTheHolyWar'':
*** Seliph and Princess Julia seem instantly attracted to each other upon meeting, but it turns out that [[spoiler:Julia is Seliph's inbreed 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 RelationshipValues 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 WordOfGod to be a distant cousin.
** In ''VideoGame/FireEmblemAwakening'' it was implied that Lissa was smitten with a man posing as Marth who had saved her from [[NotUsingTheZWord Risen]]. [[spoiler: Turns out 'Marth' was actually Lissa's ''niece from the future''.]]
** In ''VideoGame/FireEmblemFates'', [[spoiler:the Male Avatar]] gets a nice dose of ShipTease with [[spoiler:Azura]]...and then the GoldenPath reveals they're cousins. And since TheReveal 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 TheReveal ''only'' happens in the GoldenPath: they could theoretically marry in ''any'' of the paths, meaning in two of them they never find out they're cousins.
* Shows up occasionally in works made with ''VideoGame/TheSims2'': unattended children can be taken away by a social worker, and then adopted into a different family. The adoption code nukes the family connection to the birth parents and creates one with the adoptive parent(s). Some players have used this loophole to have siblings, and twins, adopted into different families, strike up romances. Since there's no genetic penalty for incest, they can even have kids. [[http://www.moreawesomethanyou.com/smf/index.php/topic,11779.0.html Read all about it]].
* In the [=PS2=] adventure game ''VideoGame/ShadowOfDestiny'', 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.
* The CasualVideoGame ''VideoGame/VirtualVillagers'' 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.
* Used in ''VideoGame/NoMoreHeroes'' when [[spoiler: Travis is informed that his ex-girlfriend Jeane, who he did sleep with, was his half-sister, which she knew beforehand. He reacts appropriately]].
** Just to drive home how creepy this trope is, the whole story was ''[[BreakingTheFourthWall told in fast-forward]]'', so as not to "jack up the age rating of the game even further" and doom it to be delayed as "[[VideoGame/DukeNukemForever No More Heroes Forever]]".
* In the first ''VideoGame/KillerInstinct'' 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.
* In ''VideoGame/{{Fallout 4}}'', you learn that all 3rd Generation [[ArtificialPerson Synths]] are created using DNA from your baby, Shaun. This turns a romance with Curie, Magnolia or [[spoiler: Paladin Danse]] towards this trope .
* At the end of the True Pacifist route of ''VideoGame/{{Undertale}}'', the married dog couple Dogamy and Dogaressa are briefly concerned that [[spoiler: their parents having melded into the Amalgamate Endogeny]] might technically make them siblings. They conclude that since they're dogs, [[SubvertedTrope they don't have an incest taboo anyway, so it doesn't matter]].
* In ''VideoGame/CrusaderKingsII'' 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.
* The trope image comes from ''VisualNovel/ApolloJusticeAceAttorney'' where 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 [[VisualNovel/PhoenixWrightAceAttorneyDualDestinies following]] [[VisualNovel/PhoenixWrightAceAttorneySpiritOfJustice entries]] although the latter does include [[TheStinger 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.

* Happens twice to Dave Strider in ''Webcomic/{{Homestuck}}''. He used to hit on Rose (ironically) before learning that they were brother and sister. In Act 6, he and Rose see their [[spoiler: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 ''Webcomic/BlackAdventures'', Black has a crush on his childhood friend White, and is shocked to learn from Mom that she's his twin sister, [[SolomonDivorce 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 ''Webcomic/{{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 ScrewTheRulesIHaveSupernaturalPowers.
* In ''Webcomic/ArthurKingOfTimeAndSpace'', Arthur sleeps with Morgan (in the space arc) and Morguase (in the baseline arc) without realising 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 realised that her spell wouldn't work properly.)
* Played for laughs in ''WebComic/AwkwardZombie'' in one comic, where [[VideoGame/FireEmblemAkaneia Marth]] finds himself attracted to [[VideoGame/FireEmblemAwakening Lucina]]. When she reveals that she's his (very distant) descendant, Marth realizes that explained his attraction perfectly: Awkward Zombie's [[AlternativeCharacterInterpretation version]] of Marth is a narcissist.

[[folder:Web Original]]
* The original plot of WebVideo/TheNostalgiaChick's "Thanks For The Feedback" would have been a parody of Luke and Leia, with she and WebVideo/TheNostalgiaCritic finding out they were related after having sex.
* In ''WebVideo/ComixFromTheUnderground'', 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 [[BrotherSisterIncest brother and sister]].
* A half-example happens in ''WebVideo/DragonBallZAbridged'', that is possibly an {{Homage}} to ''Film/BackToTheFuture''. 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. *winks suggestively*\\
'''Trunks''': *keeps smiling while [[ScreamingAtSquick screaming in his head]]*
** Upon finding out the truth a few years later:
--->'''Bulma:''' Oh my god, I solicited my son for sex.
* ''Podcast/RandomAssault'': The other hosts claim Drew has a lot of surprise sex with his 2 younger brothers.

[[folder: Western Animation]]
* Used in every Creator/SethMacFarlane shows.
** ''WesternAnimation/FamilyGuy'':
*** 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 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 [[Franchise/{{Transformers}} 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. [[{{Squick}} 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.
** ''WesternAnimation/AmericanDad'' had a version of this in an episode where Roger painted a nude portrait of Hayley for an art class, then rented it out to Steve as [[ADateWithRosiePalms masturbation material]][[note]]he didn't know it was her because the painting stopped at her lips[[/note]]. Hayley is naturally {{Squick}}ed 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 ''WesternAnimation/TheClevelandShow'', 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.
* The episode "Roswell that Ends Well" in ''WesternAnimation/{{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 [[spoiler: [[StableTimeLoop Fry himself]]]].
* In ''WesternAnimation/GIJoeARealAmericanHero'', 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.
* {{Averted|Trope}} on ''WesternAnimation/KingOfTheHill:'' Joseph is getting closer to a girl who is actually his half-sister. To prevent them from actually doing anything, Peggy [[InvokedTrope invokes]] FriendVersusLover with Bobby, making sure he's always hanging around them so that they can't actually do anything together.
** Also {{Averted}} in another episode: [[ThisLoserIsYou 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.
* One of the episodes in ''WesternAnimation/MikeTysonMysteries'' involves a couple who doesn't want their daughter to marry a man. As it turns out, the man is the husbands son from [[HalfHumanHybrid 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.
* An episode of ''WesternAnimation/TheSimpsons'' 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 "[[HeelRealization Dear God, I'm an abomination!]]"
* Played for laughs in ''WesternAnimation/TeenageMutantNinjaTurtles1987.'' 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 SeparatedAtBirth 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 ''WesternAnimation/TeenageMutantNinjaTurtles2012''. [[TheLeader Leonardo]] and [[DarkChick Karai]] have a very DatingCatwoman relationship. It's later revealed that [[spoiler: Karai is Splinter's daughter, making Leo her brother by adoption (unless fan-theories of the mutagen making the turtles Splinter's biological sons are correct)]].

[[folder:Real Life]]
* There was [[http://en.wikipedia.org/wiki/Cecil_Jacobson 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.
* A Minnesota school hosts a pep assembly. Part of it is having various athletes receiving blindfolded special kisses from a secret admirer... [[http://articles.nydailynews.com/2011-12-16/news/30526908_1_pep-rally-viral-videos-prank 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 [[http://www.spoliamag.com/the-time-casanova-almost-accidentally-married-his-daughter/ 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 [[ParentalIncest impregnated]] the daughter with their [[RefugeInAudacity 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 [[http://www.iep.utm.edu/lenclos/ 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 [[BreakHisHeartToSaveHim 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 AwfulTruth: "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 [[http://www.guardian.co.uk/uk/2008/jan/11/allegrastratton 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...
%%* [[http://www.reddit.com/r/AskReddit/comments/23tp3i/what_is_the_most_awkward_accidental_physical/ch0qxvz This unfortunate anecdote]] from {{Website/Reddit}}.
* Due to {{UsefulNotes/Iceland}} having a rather small population with no last names, there is apparently a smartphone app meant solely to avert this trope.