Bob and Janet are siblings. So are Spencer and Alice. Alice marries Bob, while Janet falls in love with Spencer. This would also work if Alice and Janet were sisters, and Bob and Spencer were brothers. Then Alice would marry one brother, and Janet would marry the other. In other words, a pair of siblings marry another pair of siblings. Someone marries the sibling of their own sibling's spouse. A quick way to achieve WeddingsForEveryone. Or if the weddings don't take place at roughly the same time, the first wedding provided the ideal opportunity for the second couple to get to know each other. Another variant, popular in the RomanceNovel, is that the first couple dies, leaving a child, and the second couple meet, argue, and finally marry because of their dispute over custody.

This can lead to a major TangledFamilyTree as the children of one couple are "double cousins" of the children of the other. Since they are as genetically similar as half-siblings, KissingCousins is even more discouraged in such cases. This gets ramped up in cases of one or two sets of identical twins being involved, in which case the cousins are biologically as close as full siblings.

A popular way to resolve a SiblingTriangle.

Not to be confused with BrotherSisterIncest or SettleForSibling (although overlap with the latter is certainly not impossible).
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!!Examples:

[[foldercontrol]]

[[folder: Anime and Manga ]]

* In ''Manga/WildRock'', Yuuen's brother and Emba's sister meet during their ceremony, which leads to the BabiesEverAfter chapters.
* In ''{{Mahou Sensei Negima}}'s'' finale, it's shown that the twins Fuka and Fumika ended up marrying twin princes from the magic world.
* In ''Manga/{{Otoyomegatari}}'', twins Leyli and Layla marry a pair of brothers. Their father [[ArrangedMarriage organised]] it deliberately so he could get rid of them both at the same time.
[[/folder]]

[[folder:Ballads]]
* In the ChildBallad ''Rose the Red and White Lily'', a pair of sisters and a pair of brothers -- their stepbrothers -- fall in love. It ends with the king ordering the two couples to marry.
[[/folder]]

[[folder: Comics ]]

* This is sometimes the origin for [[Franchise/{{Spider-Man}} Peter Parker]]'s Aunt May and Uncle Ben's relationship with his parents. Originally, Uncle Ben was just Richard Parker's considerably older brother and Aunt May and Mary Fitzpatrick-Parker were unrelated, but some recent versions have the women as sisters as well.
** This is specifically hinted at in ''ComicBook/UltimateSpiderMan'', where Aunt May refers to her sister's death and calls Peter her sister's responsibility during a fight.
** Explicitly done in MarkMillar's ''Trouble'', one of several reasons it was immediately declared CanonDiscontinuity.
** In the regular continuity, however, it's often noted that this is not the case, and Aunt May (Reilly, not Fitzpatrick) and Peter Parker are not related by blood at all, making her selfless love and doting nature all the sweeter.
[[/folder]]

[[folder: Fan Fiction ]]

* In a series of books about ''Disney/TheLionKing'', Simba and Nala have a son, Kopa, thus making him Kiara's brother. Guess who Kovu's sister, Vitani, is almost always paired up with.
* In ''FanFic/HowIBecameYours'', Zuko gets together with Katara and Azula with Sokka.
* Many ''Franchise/{{Digimon}}'' fanfics and fans ship both Taito (Taichi and Yamato) and Takari (Takeru and Hikari)
* Many ''Series/{{Supernatural}}'' fans/fanfics that ship Sam and Gabriel also ship Dean and Castiel.

[[/folder]]

[[folder: Fairy Tales ]]
* The eponymous sisters of Creator/TheBrothersGrimm tale "Literature/SnowWhiteAndRoseRed" married princes who were brothers.
* In KingArthur mythology, brothers Gareth and Gaheris married sisters Lyonesse and Lynet.
* In Creator/JosephJacobs's ''Literature/KateCrackernuts'', Kate, having rescued the sick prince, finds that her stepsister Anne and the prince's brother had fallen in love at first sight.
* In Creator/AsbjornsenAndMoe's ''Literature/TheGiantWhoHadNoHeartInHisBody'', there's a ''six-fold'' in-law marriage: six brothers marry six sisters, with only the youngest brother marrying a different bride.
* In the oldest variant of ''Literature/BeautyAndTheBeast'', Beauty and the Beast are the children of such marriages, between two royal brothers and two fairy sisters.
* In ''Princess Belle-Etoile'', a king and his brother marry two sisters. Unfortunately, there is a third sister and the king and his brother don't have a third brother for her. She marries an admiral instead and becomes jealous. (Their children, three of the king's and one of the brother's, are then abandoned together, and despite being raised as brothers and sister, [[KissingCousins the king's daughter and the brother's son manage to fall in love and end up married]].)
* In the Arab fairy tale, "The Father of Seven Sons", the father takes it into his head that his sons must marry seven sisters. He does find such brides for them.
** Other Arab fairy tales reflect the tradition of KissingCousins; a woman falls in love with a man and that's a problem because she's betrothed to her first cousin. If he's willing to give her up, this is often amiably resolved by the new bridegroom offering the cousin a bride who is his cousin.
* In the Sicilian fairy tale ''Cacciaturino'', a widowed king and a widowed queen, and at the same time, her seven sons marry his seven daughters, for an eight-fold marriage.
[[/folder]]

[[folder: Film ]]

* ''Film/{{The Birth of a Nation}}'' ends with Phil Stoneman, his wife Margaret, her brother Ben Cameron, and his wife Elsie, who happens to be Phil's sister, on a double honeymoon.
* ''Film/{{Twins}}'' ends with the eponymous twins marrying sisters and each having twins of their own.
[[/folder]]

[[folder: Literature ]]

* Creator/JaneAusten loves this trope:
** ''Literature/NorthangerAbbey'': John and Isabella Thorpe plan to marry Catherine and James Moreland, respectively, but ultimately don't because John is a pompous windbag and Isabella is an incurable flirt.
** ''Literature/SenseAndSensibility'': John Dashwood and his half-sister Elinor Dashwood marry sister and brother Fanny and Edward Ferrars. John and Fanny are already married before the book begins, but Elinor and Edward don't get married until the end (Edward's ArrangedMarriage and ChildhoodMarriagePromise to Lucy were in the way).
** ''MansfieldPark'': Mrs. Grant plans for her brother and sister Henry and Mary Crawford to marry siblings Julia and Tom Bertram. They both blow it, starting by flirting with the other two Bertrams Maria and Edmund. Note to [[ShipperOnDeck Shippers On Deck]]: Make sure the sides are balanced before attempting this trope. Ironically, at least 2 {{Fan Sequel}}s -- ''Susan Price'' and ''Mansfield Revisited'' -- invoke this trope by marrying Fanny's sister Susan Price to Edmund's brother Tom Bertram.
** ''{{Literature/Emma}}'': Brothers John and George Knightley marry sisters Isabella and Emma Woodhouse. As in ''Literature/SenseAndSensibility'', the heroine's marriage takes place at the end, while her sibling's marriage took place before the start of the book, so Emma and her Mr. Knightley have been LikeBrotherAndSister all her life.
* At the very beginning of ''ASongOfIceAndFire'', best friends King Robert and Ned Stark intend to do this. They had already betrothed Sansa and Joffrey, while Robb and Arya escorted Myrcella and Tommen to dinner, with the implication that they were trying to set them up. Later Catelyn Stark makes a contract with Walder Frey for Robb and Arya to marry two Frey siblings.
* A minor side-plot in Creator/TomClancy's ''Literature/ClearAndPresentDanger'' concerns a pair of criminal twin brothers who fell for a pair of twin sister hookers, and got sent to prison for murdering their pimp. They wind up getting out again after a little unofficial deal is struck with the police, killing a pair of Cartel Goons who were set to get off on a technicality, inside the prison. As far as we know, the two sets of twins all lived {{happily ever after}} while the main plot moved on.
* In ''Anne's House of Dreams'', Leslie's husband Dick had a "double cousin" named George who looked almost like his twin. [[spoiler: When the brain-damaged man everyone had assumed was Dick for thirteen years was cured, it turned out to be George.]]
* In Amy Tan's ''The Bonesetter's Daughter'', sisters Lu Ling and Gao Ling marry brothers Edwin and Edmund Young.
* In ''[[XWingSeries The Bacta War]]'', we learn that Lanal Darklighter is Gavin's aunt on both sides of the family, because she is both his mother's sister and his paternal uncle's wife.
* There exists somewhere an "ending" written for the ''Literature/ArabianNights'' that was made several hundred years later, in which Shahryar had magically fallen deeply in love with Scheherazade, decided to keep her, and then his brother magically fell in love with her sister so they could be one big happy family.
* Mentioned in an aside in ''Literature/ToKillAMockingbird'', although not actually featured. Atticus mentions the concept of double cousins to Scout, saying "two brothers married two sisters." She and Dill work on figuring it out, and reason that if Dill had a sister whom he married, and Jem and Scout got married, their kids would be double cousins. Only off by a little bit there...
* Used in ''Ada, or Ardor'' to set up the incestuous cousins, although they later turn out to be siblings as both were the product of an affair between the double in-laws.
* In ''{{Literature/Malevil}}'', Emmanuel's father and uncle married a pair of sisters.
* In Emily Rodda's ''Pigs Might Fly'', this happened to Enid and her sister, who met their future husbands (brothers) at the same party. This is justified as it happened during a UEF (Unlikely Events Factor) Storm, which causes [[ExactlyWhatItSaysOnTheTin unlikely events]] such as [[CueTheFlyingPigs pigs flying]].
* This shows up several times in ''Literature/TheSilmarillion'' and ''Literature/TheLordOfTheRings''.
** [[Literature/TheLordOfTheRings Sam's]] sister Marigold Gamgee married Rose's brother Tolman Cotton.
** [[Literature/TheSilmarillion Galdor]], heir to the house of Hador, and his sister Gloredhel marry Hareth of the Haladin and her brother Haldir.
** Galdor and Hareth's sons Húrin and Huor marry first cousins Morwen and Rían.
** Siblings Éomer and Éowyn of Rohan marry first cousins Lothíriel of Dol Amroth and Faramir of Gondor.
** [[Literature/TheHobbit Bilbo]]'s father (Bungo Baggins) and his first cousin Rosa married siblings Belladonna and Hildigrim Took. (Bilbo's and Frodo's fathers were first cousins once removed, and their mothers were aunt and niece -- look through the family trees at the end of ''Literature/TheLordOfTheRings'' and you can find endless cases of people marrying their in-laws as well as KissingCousins.)
* In ''Literature/ShanghaiGirls'' by Lisa See, sisters Pearl and May marry brothers Sam and Vern Louie, and Pearl has a daughter. [[spoiler: Subverted because Sam is not really Vern's brother, he was adopted by the Louie family so he could get to America, and Pearl's daughter is really May's daughter with another man.]]
* In Jacqueline Wilson's ''Double Act'', Garnet has always assumed she and her twin sister Ruby would marry a pair of twin boys.
* ''Literature/ABrothersPrice'' has this trope seen as very positive, since it means closer bonds between families and makes cousins more like sisters. When Cullen is married to the older Whistler sisters, he hopes to get their cousins married to ''his'' sisters.
* In Creator/AletheaKontis's ''Literature/{{Enchanted}}'', a pair of sisters marry, not a pair of brothers, but a father and son, so they are stepmother-in-law and stepdaughter-in-law.
* Book 4 of ''TheFaerieQueene'': Brother and sister Campbell and Canacee married sister and brother Cambina and Triamond.
* [[WhatKatyDid In the High Valley]] by Susan Coolidge: Lionel and Imogen Young marry Joanna and Dorry Carr. Lionel describes it as 'change partners all round and down the middle'
* First {{Lensman}} Virgil Samms and his cousin George Olmstead are (allegedly) remarkably similar in appearance because of a two-generation stack of this phenomenon. Supposedly, "quadruple first cousins" is the closest the genealogists could come to computing what had actually happened.
[[/folder]]

[[folder: Live Action TV ]]

* ''{{Roseanne}}'': [[TomboyAndGirlyGirl Darlene and Becky Conner]] married [[SiblingYinYang David and Mark Healy]], respectively.
-->'''David:''' [[DeadpanSnarker Thanks for making me and my girlfriend related]].
** Or [[spoiler:[[AllJustADream the other way around]]]], according to the finale.
** The characters had a lot of fun joking about David and Darlene's relationship after they essentially adopted him as a member of the family long before Becky got married. To the point where when Darlene and David get engaged Roseanne celebrates the fact that they are officially the most redneck white trash in town.
* In ''LostInAusten'', after Mr. Collins marries Jane, he tries to marry his brothers off to the younger Bennett sisters. It doesn't quite work out.
* ''IntoTheWest'' used this in the first episode.
* ''Howe & Howe Tech'' is about a company run by identical twin brothers Mike and Geoff, with their wives, Tammy and Tracy, handling office work. Tammy and Tracy are sisters.
* Played with on ''Series/LosHombresDePaco''. Paco and Pepa are brother and sister and Silvia and Lola are sisters. Paco and Lola were married but got divorced before [[LesYay Pepa and Silvia]] got married later on in the series.
* ''GilmoreGirls'' had one episode where the Inn hosted a double wedding between two sets of twins.
* ''Series/MarriedWithChildren'': In "How to Marry a Moron", Kelly is engaged to a rich guy named Lonnie Tot and Lonnie's ugly sister is interested in Bud. When Lonnie's Dad says he'll make Al his business partner if both marriages take place, Al eagerly announces Bud's engagement.
[[/folder]]

[[folder: Religion and Mythology ]]

* A rabbinic legend says that ''Literature/TheBible'''s Laban intended to marry his two daughters to their [[KissingCousins two male cousins]]--the older two, Leah and Esau, would be one couple and Jacob and Rachel would be the other. {{Averted}} because Leah prayed to {{God}} that she wouldn't have to marry the wicked Esau, and He arranged for both sisters to marry Jacob instead.
* According to Josephus, Levi and Issachar married two sisters named Adinah and Aridah, while their brothers Gad and Naphtali married sisters named Merimit and Uzit.
* In ClassicalMythology there were the Danaids, fifty sisters, who were in a mass ArrangedMarriage to [[KissingCousins their fifty male cousins]]. They are eventually compelled to go through with the marriages, and then [[spoiler:all but one of the sisters murder their husbands in their sleep]].
* Also in Greek ClassicalMythology, brothers Menelaus and Agamemnon married half-twin-sisters (different fathers, [[DoubleStandardRapeDivineOnMortal don't ask]]) Helen and Clytemnestra, respectively.

[[/folder]]

[[folder: Tabletop Games ]]


* The Clothar race in {{Traveller}} always has these. Clothar are born as a brother sister pair of mindlinked twins and each pair marries another pair creating what amounts to a quadruple marriage rather then a dual marriage. As each pair is telepathic, effectively everyone knows everything about the others marriage.

[[/folder]]

[[folder: Video Games ]]

* Doable in ''[[VideoGame/FireEmblemTheSacredStones Fire Emblem: The Sacred Stones]]'', pairing Prince Ephraim with Princess Tana and Ephraim's twin sister Princess Eirika with Tana's older brother Prince Innes.
** Also doable in the second generation of ''Genealogy of the Holy War'' with, well, any two brother-sister pairs, but notably [[FanPreferredCouple Arthur with Fee and Sety with Tinny]]. This can also potentially be two pairs of KissingCousins if you pair Patty with Lester and Faval with Rana.
*** It's actually ''worse'' than KissingCousins if you pair those last two couples together; their mothers were twin sisters, so you're actually [[BrotherSisterIncest marrying two pairs of genetic half-siblings to each other]].
*** Can be done in many varieties in ''VideoGame/FireEmblemAwakening'' with the second generation, all involving Lucina, Chrom!Inigo or Chrom!Brady and a family consisting the male Avatar and a woman who has a son. (For example, Avatar!Gerome can marry Lucina and his younger sister Morgan goes for Chrom!Inigo, or Avatar!Inigo can marry Lucina and Morgan marries Chrom!Brady. [[KissingCousins Add Owain to the mix and things can get even zanier]].)
* A sidequest in ''VideoGame/FinalFantasyXII'' revolves around preventing this situation. A group of seven [[PrinceCharmless Archadian nobles]] who are all brothers are trying to force a group of seven sisters who work as airship stewardesses to marry them.
* A possible marriage outcome in ''VisualNovel/LongLiveTheQueen''. If Elodie has shown interest in [[spoiler:Brin, Duchess of Hellas]] who is a lesbian by preference, she suggests that they can be together if [[spoiler:Brin marries Elodie's father and Elodie marries Brin's brother.]] This gets very confusing for any resulting children.
[[/folder]]

[[folder:Webcomics]]
* In ''{{Erstwhile}}'', when Rose Red confides her problems with marrying when she and her sister ought to always share, the bear suggests that she marry a man with a brother who can marry her sister. [[spoiler:That's how it ends.]]
* In [[http://trialofthesun.com/ Trial of the Sun]], Rennin and Caliosis end up marrying each other's sisters: Rennin set up his good friend with his sister out of gratitude, and much later married Cal's sister Filumena when Filumena's marriage prospects had otherwise weakened.
[[/folder]]

[[folder: Western Animation ]]
* A Disney ''[[WesternAnimation/SillySymphonies Silly Symphony]]'' ended like this. Two feuding royal families make peace, and the king and the prince of one kingdom marry respectively the queen and princess of the other kingdom (by the way, they were also all anthropomorphic musical instruments).
* An episode of ''WesternAnimation/TheSimpsons'' has Homer's father courting Marge's mother. Homer realizes that if they end up getting married (as they very nearly do), he and Marge will be brother and sister. He freaks out at the implications.

[[/folder]]

[[folder: Real Life ]]

* Anthropologists call (one type of) this Brother-Sister Exchange, such as the Mundugumor of New Guinea.
** The Yanomami do this a lot: A man marries his sister's husband's sister. [[KissingCousins The children of one marriage then typically marry the children of the other.]] Happens a lot with moieties (two groups which must marry someone of the other group).
* Romans, especially the rich upper classes, would often do this, with daughters as bargaining pieces to enforce alliances. Just look at the family of the Julio Claudian Emperors, for example. This tradition carried over to the medieval era, with most royal families engaging in this.
* The most famous Siamese Twins (now referred to as ConjoinedTwins), Chang and Eng Bunker, married sisters.
* It doesn't come up in [[Literature/LittleHouseOnThePrairie her own books]], but Laura Ingalls Wilder's parents were the second of three marriages between their families: Uncle Henry was Ma's brother and his wife, Aunt Polly, was Pa's sister, while Aunt Eliza was Ma's sister and Uncle Peter was Pa's brother.
* There was a question on Yahoo Answers once (quite possibly {{Troll}}ing, or at least posing a thought experiment) about a pair of identical twins who'd married ''another'' set of identical twins and wanted to set up an ArrangedMarriage between their respective children. Once you've gotten over the initial instinct to reach for the BrainBleach and done a bit of basic maths, you realise the kids in question would be, genetically speaking, [[BrotherSisterIncest full siblings]]. Yeeah. There was a case in the UK of one set of identical twins marrying another, not that they planned it like that. One marriage apparently ended in divorce.
* UsefulNotes/SigmundFreud's wife Martha Bernays was the sister of Ely Bernays, who married Sigmund's sister, Anna Freud (making public relations pioneer Edward Bernays Freud's 'double nephew').
* These marriages were popular among peasants in early modern France in the brother-and-sister marry brother-and-sister form. Whereupon the two brides, in lieu of a dowry, would sign over to each other their respective inheritance rights.
* Averted in the case of the Dionne quintuplets (the first ever surviving set of quintuplets, all girls): Dr. Allan Roy Dafoe, who had charge of them through their tenth year, was convinced that they would never marry because there was no set of identical ''male'' quintuplets. Three did eventually marry men not related to one another; one became a nun (and died young, to boot); one devoted herself to her work and never married.
* Almost happened with NapoleonBonaparte and his elder brother Joseph : Joseph married Julie Clary, the daughter of a wealthy silk merchant, in 1794 and Napoleon fell in love and became engaged with Désirée, Julie's younger sister. However, Napoleon and Désirée broke up when Napoleon married Joséphine and the rest is history.
* During the royal wedding of Prince William and Kate Middleton their younger siblings PrinceHarry and Pippa Middleton get really close. This pair ended up rumor only though.
[[/folder]]

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