History Main / RelativeError

* The divergences in ''Fanfic/WithThisRing'' include Superboy being adopted by Wonder Woman, who of course [[TheAgeless looks not much older than him]] (and people [[DistractedByTheSexy do look]]). Some of his school peers wonder if he's cheating on "Megan" (Miss Martian) when they see Diana hug him and kiss his forehead, until they find out what's actually going on.

* In the ''VideoGame/FateGrandOrder'' fan comic ''[[https://m.imgur.com/gallery/6kuTgtA How Complicated Can This Family Tree Get]]'', Artoria finds Lostbelt Morgan and Lancelot and accuses him of making a move on her sister. Lancelot protests that, one, he wasn't making a move on anyone, and two, that he was speaking to his adoptive mother Nimue, much to his king's confusion. Morgan then says that the Proper Human History versions of Morgan and Nimue are both the same person, specifically split personalities. Lancelot then leaves after realizing that the king he secretly held impure thoughts towards ([[ItMakesSenseInContext including getting her older self into a bunny suit]]) was actually ''[[SurpriseIncest his adoptive aunt]]''.

* In an episode of ''Series/GilmoreGirls,'' when Richard is in the hospital, Michel hijacks Sookie's concerned phone call to inform Lorelai that a "couple" who checked into the Dragonfly Inn is actually a brother-sister pair.

* Chuck Berry's song "Memphis, Tennessee" is built on getting the listener to make this error, and then surprising them. He sings about a girl he misses, and how they were parted because of her mother, and he's trying to get in touch with her. In the second-to-last line, he sings "Marie is only six years old" and suddenly you realize Marie is his daughter, not his ''Love Interest''.

This is somewhat the inverse of, but definitely comparable to, LikeBrotherAndSister--in which they have a close, platonic, but non-genetic relationship. If the characters ''themselves'' don't know, it's SurpriseIncest. If their resemblance to a romantic couple is particularly convincing, there may be IncestSubtext at work; if it's more convincing than the idea that they're brother and sister even to the audience who's already in on the secret, that's probably a RelationshipWritingFumble. Sometimes though, it [[BrotherSisterIncest happens to be]] [[NotWhatItLooksLike Exactly What It Looks Like]].

* ''Fanfic/FateHaremAntics'': Rin Tohsaka thinks that Caren Hortensia is Kirei Kotomine's lover instead of his daughter. Since Caren hates Kirei, she has no problem playing it up to make him look like a pedophile.

* Inverted in the ''Series/BuffyTheVampireSlayer''/''Series/{{Supernatural}}'' fanfic ''[[http://www.tthfanfic.org/wholestory.php?no=18482 Runs in the Family]]'', where Xander asks Sam and Dean if they're brothers, which Dean interrupts with "Dude! We are NOT gay!" Given the number of times they've been asked if they're together in the actual series, his reaction is understandable.

* In ''VideoGame/FateGrandOrder'', Miyamoto Mushashi teases Fuuma Kotarou for sneaking glances at [[spoiler:Katou Danzou]], thinking he has a crush on her. [[spoiler:He later explains to Musashi that Danzou was his surrogate mother]].

* Inverted for Helen Slater and Creator/ChristianSlater. For years, thanks to them playing siblings in the movie ''Film/TheLegendOfBillieJean'', the former has had to constantly tell curious fans that they're not actually brother and sister.

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* Inverted in ''Manga/EvenThoughWereAdults''. Ayano initially mistakes Akari's husband for her brother. She didn't know that Ayano was married.

* In ''Series/DesperateHousewives'', Lynette pretends to be a teenage girl in a chatroom so she can have real conversations again with her son. Unfortunately, he gets a crush on her online persona and she has to let him down easy with a goodbye message...[[WhatAnIdiot which she signs "Love, Mom."]]

* Inverted in the ''Series/BuffyTheVampireSlayer''/''Series/{{Supernatural}}'' fanfic ''[[http://www.tthfanfic.org/wholestory.php?no=18482 Runs in the Family]]'', where Xander asks Sam and Dean if they're brothers, which Dean interrupts with "Dude! We are NOT gay!". Given the number of times they've been asked if they're together in the actual series, his reaction is understandable.

* A vendor in ''Fanfic/MyMasterEd'' assumes Edward and Hohenheim are brothers. Hohenheim is under the impression their similar appearance is a coincidence and they aren't related at all. Only Edward himself knows they're [[KidFromTheFuture father and son]].

* ''Film/KullTheConqueror'': Kull assumes Ascalante to be Zareta's lover since he's so keen on rescuing her. When he asks Zareta directly about their relation to each other, she reveals that Ascalante is her brother. She later becomes Kull's lover, which Ascalante is totally fine with.

* Inverted in the Creator/WinonaRyder film adaptation of ''Literature/LittleWomen''. A suitor of Jo's calls at the house and is informed that "Ms. March and her husband live next door". He assumes Jo has married someone else but Jo hurries down the road after him to explain that it's her sister who is married.

* In one of Anne Perry's Late Victorian mysteries a married man is seen with a pretty young woman who he obviously cares for very much. It turns out she is his daughter, his ''Legitimate'' daughter, his second marriage is bigamous and his four children by it illegitimate. Ouch.

* ''Series/BoardwalkEmpire'': New York gangster "Lucky" Luciano and Atlantic City gangster Jimmy Darmody quickly develop a mutual dislike of each other. So when Luciano meets a stunning redhead who introduces herself as "Mrs. Darmody", Luciano quickly makes the moves on her, assuming she's Jimmy's wife. When his boss Rothstein calls him up, he's quite amused, telling Luciano he didn't bang Jimmy's wife, he banged Jimmy's ''mother''. Who later on even helps out her boy with luring Luciano into a trap.

* {{Exploited|Trope}} and PlayedForDrama in the ''Series/ColdCase'' episode "Thick As Thieves". As the detectives eventually find out, the VictimOfTheWeek and her boyfriend were a team of con artists who claimed to be a couple as part of their swindling strategy when the truth is the "boyfriend" was the victim's ''son''.

** Rachel is shocked that her boyfriend seems to be cheating on her, only to find that the woman he was hugging was his sister. [[spoiler:Then Rachel goes to their apartment and finds them tickling each other, eating whipped cream from each others' laps and, ultimately, sharing a bath together. Her boyfriend insists that it's all innocent and just proof that they're close enough as siblings to behave as they did as kids, Rachel thinks it's too weird and leaves him.]]
** Siblings Ross and Monica Geller, who in spite of never having on-screen moments that may confuse people, are horrified to learn in the tenth season that they had actually kissed while teenagers (It was dark, Ross thought he was kissing Rachel, Monica thought he was her "Midnight Mystery Kisser").

* In ''Series/TrueBlood'', Violet Mazurski assumed Jason Stackhouse was cheating on her when she saw him hanging out with Sookie until he told her Sookie is his sister. Violet's response, "Then you're my sister too!" and then kissing her on the lips.

* In the opera ''Theatre/{{Rigoletto}}'', the courters learn that Rigoletto secretly has a young woman living in his house. They assume she's his mistress, kidnap her and give her to the lecherous Duke to humiliate the hated jester. As it turns out, she's his innocent, virginal daughter, and his response to her kidnapping isn't embarassment, but vengeful PapaWolf rage.

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* " In the ''VideoGame/FateGrandOrder'' fan comic ''[[https://m.imgur.com/gallery/6kuTgtA How Complicated Can This Family Tree Get]]'', Artoria finds Lostbelt Morgan and Lancelot and accuses him of making a move on her sister. Lancelot protests that, one, he wasn't making a move on anyone, and two, that he was speaking to his adoptive mother Nimue, much to his king's confusion. Morgan then says that the Proper Human History versions of Morgan and Nimue are both the same person, specifically split personalities. Lancelot then leaves after realizing that the king he had impure thoughts towards was actually ''his adoptive aunt''.

* ''WesternAnimation/{{Jem}}'': Aja and the others make this error in "Britrock". Aja's boyfriend starts acting more quiet than usual and tells her he has to tell her a secret he's been keeping. When Craig tells Aja Stormer is his secret Aja gets mad and it only gets worse when he introduces himself as "Craig Phillips" and Stormer as "Mary Phillips". Even Craig's bandmates lampshade how badly Craig went about the situation and decide to [[GoingToTheStore leave the room]]. Aja slaps Craig and runs away crying. It isn't until a moment later that Kimber informs her Stormer is Craig's ''little sister'', not his wife. Craig had been hiding the fact because The Misfits and The Holograms are [[TheRival bitter enemies]]. Apparently, the fact Craig and Stormer are [[YouGottaHaveBlueHair the only characters with deep blue hair]] went unnoticed by Aja.

* In the ''VideoGame/Persona3'' fic [[https://www.fanfiction.net/s/13633431/1/Wh-WHAAAAAAAAAAT Wh-WHAAAAAAAAAAT]], a rumor is spread around Gekkoukan High School that Makoto and Yukari have a child after they were spotted hanging around a child by the Naganaki Shrine, who Makoto referred to as their family. The child in question was Ken, who Aegis points out is ten-years-old, much older than the year Makoto was even in Gekkoukan, much less dating Yukari.

** In ''Blood Rites'', between Thomas Raith and [[spoiler:Harry Dresden]], made worse by the fact that 1) they cannot openly reveal their true relationship, and 2) they were sharing the latter's small apartment for an extended period after ''Literature/BloodRites''. And 3) Thomas was deliberately pretending to be gay in his public life for completely unrelated reasons. Considering all this together, we should have seen it coming from the paragraph after that ''Wizard of Oz'' poster on Thomas's wall.

* " In the ''VideoGame/FateGrandOrder'' fan comic ''[[https://m.imgur.com/gallery/6kuTgtA How Complicated Can This Family Tree Get]]'', Artoria finds Lostbelt Morgan and Lancelot and accuses him of making a move on her sister. Lancelot protests that, one, he wasn't making a move on anyone, and two, that he was speaking to his adopting mother Nimue, much to his king's confusion. Morgan then says that the Proper Human History versions of Morgan and Nimue are both the same person, specifically split personalities. Lancelot then leaves after realizing that the king he had impure thoughts towards was actually ''his adopted aunt''.

* In ''VideoGame/FateGrandOrder'', Miyamoto Mushashi teases Fuuma Kotarou for sneakingglances at [[spoiler:Katou Danzou]], thinking he has a crush on her. [[spoiler:He later explains to Musashi that Danzou was his surrogant mother]].

* ''Film/GMen'': When Brick, who has become attracted to Kay, learns she's waiting to see Jeff (his boss), he's unhappy at first, but when he learns Kay is Jeff's sister, he smiles.

* Inverted in ''Manga/OtonaNiNatteMo''. Ayano initially mistakes Akari's husband for her brother. She didn't know that Ayano was married.

* " In the ''VideoGame/FateGrandOrder'' fan comic ''[[https://m.imgur.com/gallery/6kuTgtA How Complicated Can This Family Tree Get]]'', Artoria finds Listbelt Morgan and Lancelot and accuses him of making a move on her sister. Lancelot protests that, one, he wasn't making a move on Morgan, and two, that he was speaking to his adopting mother Nimue, much to his king's confusion. Morgan then says that the Proper Human History versions of Morgan and Nimue are both the same person, specifically split personalities. Lancelot then leaves after realizing that the king he had impure thoughts towards was actually ''his adopted aunt''.