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Basically the step up from YourCheatingHeart, but not up there with a concubine. It's a girlfriend for an already married man. Sometimes the affair is public, but just as often is not.

The reasons can vary. Often the husband just doesn't care enough for his wife, especially if there was an ArrangedMarriage. Sometimes it's actually expected in a culture (even if not actually said). Sometimes the wife can even drive the husband to this, but just as often she can be a kind woman, or even a HotConsort.

Sometimes the mistress will be happy with her position, but sometimes she will want the husband to leave his wife and marry her. Sometimes the latter could even lead to trying to [[MurderTheHypotenuse outright get rid of the wife]]. Needless to say, if the wife wasn't aware of her existence and finds out about her, the mistress is very likely to be killed at her hands, if the husband isn't the one to die that is.

Crime Fiction stories often involve this, as it conveniently gives everyone involved a motive for murdering at least ''one'' of the LoveTriangle. The more mistresses, the more potential red herrings/victims.

[[TruthInTelevision There are a LOT of historical examples]], because European aristocratic marriages were almost always purely political. It was generally accepted that the husband and ([[DoubleStandard though less tolerated]]) wife would take lovers to provide the emotional fulfillment they would not be getting from their marriage. It was usually considered bad form to be public about it, but not always. In some countries, such as France, the mistress was even something of a semi-official position. Formalizing and legitimizing it made things less awkward in public, and it also made it easier to keep tabs on any illegitimate children that might one day contest the throne.

%%'''Remember, this has to be a mistress, not just an affair. That's YourCheatingHeart.'''

Compare TheUnfairSex, OopsIForgotIWasMarried (if the mistress does not know about the other's family), DarkMistress (who is ''not'' an evil version of this, despite the name).

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!!Examples:

[[foldercontrol]]

[[folder:Anime and Manga]]
* This trope is referenced in ''Manga/RanmaOneHalf''. One of the things [[JerkWithAHeartOfGold Ranma]] does to try and get Ukyo [[PleaseDumpMe to dump him]] is to tell her he's going to go spend the night with his mistress. Made funnier when he enters Akane's room and tries to convince her to go along with it. [[{{Tsundere}} She]] really doesn't take it well.
* ''RosarioToVampire'' makes use of it overtly; in the case of those seeking Tsukune's love only one has expressed real interest in marriage, with the others either outright saying they want to be something else to him, or simply showing no great interest either way. However more subtly [[spoiler:when we finally discover the full picture of the Shuzen family, we learn that not only was [[DisappearedDad Issa]] casually polygamous, but it is implied that among his partners, Moka's mother [[LadyOfWar Akasha]] [[NamesToRunAwayFromReallyFast Bloodriver]] is Issa Shuzen's mistress rather then his wife. This despite also being a Shinso vampire and one of the Three Dark Lords, who control/watch over Japan.]]
* Nodoka gets the idea of being this in ''Manga/MahouSenseiNegima'' when [[DirtyMindReading her subconscious suggests]] a solution to a LoveTriangle she's in. That suggestion is "''saishoudoukin''," a situation where a man keeps a wife and a concubine in the same house.
* Being set at the court of Versailles in the years preceding TheFrenchRevolution, ''Manga/RoseOfVersailles'' has various examples, the most notable being Madame Du Barry (the mistress of King Louis XV and [[HistoricalVillainUpgrade an early villain]] and enemy of Marie Antoinette). At the time, [[LampshadeHanging as explained by Madame De Polignac]], it was so common for married nobles to have a lover on the side that people were ''astonished'' that Louis XVI and Oscar's father had none, and many were willing to believe that Fersen was Marie Antoinette's lover because it made more sense than Marie Antoinette refusing to consummate their love because of her duty as the queen.
** Speaking of Madame De Polignac... Her lover was ''her brother in love''.
** When it appeared that he would marry Oscar, Girodelle told Andre he would allow him to be Oscar's lover if they both wished. ''That'' is how easily it was accepted.
* ''[[Anime/{{Patlabor}} Patlabor: The Movie 2]]'': Back when [[spoiler: Shinobu]] was a cadet at the Tsuge Institute, she had an affair with the instructor, himself, despite knowing he was married. It was both a breach of police protocol and ethics. Word of the affair soon got out, reaching as far as he top brass, which created a scandal[[note]]though it isn't said whether Tsuge's wife ever found out he was cheating on her with one of his students[[/note]]. The stigma forced [[spoiler: Shinobu]] to settle for a position at the SVU, rather than a higher one more befitting her talent[[note]]had it not been for the scandal, Shinobu would have likely gained a position on the Tokyo Metropolitan Police Management Bureau[[/note]].
[[/folder]]

[[folder:Film]]
* Lola's father has one in ''Film/RunLolaRun''.
* Helen's husband Charles has one in ''DiaryOfAMadBlackWoman'' , and she even had two children with him (meanwhile Helen had two miscarriages).
* The book in ''DownWithLove'' causes even mistresses to not cooperate with men anymore.
* Sam's mistress in ''RuthlessPeople'', who tries to blackmail him because she's sleeping with another man.
* Veronica Franco becomes this to Marco Venier in ''Dangerous Beauty'', after having been a [[HighClassCallGirl courtesan]].
* In ''Film/InTheMouthOfMadness'', an InsuranceFraud scam is found out when a guy claims a warehouse full of [[PrettyInMink fur coats]] was supposedly destroyed, but he kept the coats, giving some to his wife, who ratted on him when it turned out he gave some to his mistress.
* Emilia, of ''Film/TheOtherWoman'', plays the eponymous role.
[[/folder]]

[[folder:Literature]]
* Tom's relationship with Myrtle in ''TheGreatGatsby''.
* In Katherine Kerr's ''Literature/{{Deverry}}'' series, Rhodry takes Jill as a mistress. He would have liked to marry her, and his allies do end up arranging things so she can be given a title to enable them to marry. However, fate has different plans in store for them and they can't... for reasons of destiny. It's acknowledged that this is common among the nobility due to the proliferation of political marriages; and in many cases the jilted spouse doesn't particularly mind as long as you are tactful and discreet.
* One interpretation of the poem "The Rival" by Creator/SylviaPlath (in ''ArielPlath'') is that the subject is an {{expy}} of the mistress of Plath's husband.
* ''Discworld/MakingMoney'' The bank's previous owner was the mistress of the former chairman, mentioning that as his mistress, she had the wife's approval because it got him out of her hair for a while. She was also good with numbers, which is why she remained in charge of the bank after his death. Before she passed on, she noted that standards have dropped and that now "the ability to spin upside down on a pole is considered sufficient".
* ''Literature/{{Dune}}'':
** The position is {{deconstructed}}, as Paul Atreides considers the woman who is technically his mistress as his true wife, and never consummates his official (and political) marriage with his actual wife.
** Going back a generation, Paul's mother Jessica is the 'bound concubine' of Leto Atreides, and presumably if he'd married she would have been this - but the two of them considere themselves married in everything but name.
* Petra Cotes in ''Literature/OneHundredYearsOfSolitude'', doubling as one of the three [[HookerWithaHeartOfGold hookers with hearts of gold]].
* In ''Guilty Wives'', Winnie is revealed to have been the mistress of [[spoiler:the President of France]] for some time before the action of the novel begins.
* ''Literature/ASongOfIceAndFire'' plays with this trope constantly.
** As part of the series's back story, King Aegon IV ("The Unworthy") had several semi-official mistresses, and thus several illegitimate children. As bastards, they weren't entitled to inherit, until the king legitimized them on his deathbed. Civil war resulted.
** Some high lords keep mistresses; but they have no official standing and the relationship is considered adulterous and immoral. Such mistresses are kept behind closed doors and the relationship is kept officially secret, even if it's common knowledge. (Tyrion Lannister's whore is treated in this way, though the stakes are higher: as a commoner, she must be kept secret at first lest she be used against him by his evil sister Cersei. Later, she's kept secret because his father doesn't approve of whores and threatens to hang the next one he finds in Tyrion's bed. In a sign of the hypocrisy of the series, after she betrays Tyrion, he discovers her in her father's bed as he escapes.)
** In Dorne, where looser standards of sexual morality are in play, mistresses can be given official status as Paramours. The relationships are public and have no implication of shame. Even a Dornish member of the supposedly celibate Kingsguard kept one. In some cases, a man and wife will even share a paramour.
** Daenerys Targaryen marries twice, but aside from that, has plenty of [[BiTheWay men and women]] to serve in her bed. Her first bedmates (aside from her husband and his bloodriders, who don't fit the trope) is her handmaiden Doreah, who teaches her the art of love while she's still married to Khal Drogo. Later, a mercenary named Daario Naharis kills his allies and defects to her side in hopes of getting in bed with her. Dany is happy to give him the job, which he keeps even after she remarries.
* In ''Literature/LesMiserables'', Marius's grandfather has had many mistresses over the course of his life, and believes it's better to take a woman as a mistress than to actually marry her. When Marius tells his grandfather about Cosette, his immediate advice is to keep her as a mistress instead of as a legal wife (Marius, who reveres Cosette, finds the idea of dishonoring her so much to be unspeakable).
* In Creator/CharlotteBronte's ''Literature/JaneEyre'', Rochester's past is filled with lovers -- usually rich and well-known performers, such as CÚline Varens. At the time of the novel, he says he's grown tired of keeping girlfriends. [[spoiler: After their would-be wedding is busted, Rochester offers this position to Jane. Jane realizes she could not possibly live with herself in this way, and leaves him.]]
* In ''InTheTimeOfTheButterflies'', [[UnnamedParent Papa]] has another family with three other children in addition to the four daughters he has with his wife.
* In ''The Literature/LastHeraldMageTrilogy'', King Randale's [[MindlinkMates beloved]] Herald Shavri is officially this, mainly because the option of a State Marriage had to be left open. Shavri even talked Vanyel into siring a child upon her in large part to hide the fact that a wasting disease had rendered the king sterile (little did she know that said "byblow" would marry into the [[SecretLegacy collateral line that eventually got the throne]]).
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[[folder:Live-Action TV]]
* Spoofed in ''DesigningWomen'', when they get a mistress to stop seeing a married man, but the wife was angry, because she knew about the affair and was having her own.
* In the first time in ''Series/QuantumLeap'' where Sam leapt into a woman, he was there to save "his" roommate from committing suicide over an relationship with her boss - she thought her boss would leave his wife for her, but the wife made it clear to her that she tolerated his "indiscretions" but they would never break up (and she was a former mistress of the boss herself, having broken up his previous marriage).
* An extremely rare GenderFlip version appears on ''Series/TheOfficeUS'', during the plotline where Michael thinks his girlfriend Donna is cheating on him but it turns out that the "other man" is her husband: "''I'M'' the mistress?"
* ''Series/{{Kaamelott}}'': Arthur has up to four mistresses at any given time, going from one to the other as his needs warrant. HilarityEnsues when a rumor spreads of his rebuking the queen, and each girl tries to convince him to marry her.
* ''MidsomerMurders'' loves this trope along with general adultery.
* ''Series/TheSopranos'': Almost every made guy has a "Comare" (literally "godmother" in Sicilian dialect, but slang for mistress) on top of their wives who they won't divorce for their Catholic beliefs. For the main character, it becomes a major plot device when one of his mistresses actually contacts his home pushing his wife to call it quits, albeit temporarily.
* ''DesperateHousewives'' wouldn't really be Desperate Housewives if it didn't have at least one mistress per season.
* In the ''Series/{{Firefly}}'' episode "Shindig," Atherton Wing wanted Inara for one of these. Mal [[FumblingTheGauntlet objected]], leading to a [[DuelToTheDeath sword duel over her honor]].
* On ''MyNameIsEarl'', Earl had a BadBoss with a hot blonde wife and an equally hot brunette girlfriend on the side. When Earl punches him (landing him in the hospital), the two women show up to be by his side...and find out about each other's existence. When the (soon-to-be-ex) wife is giving him a DefenestrateAndBerate, she finds the money he's been laundering and he winds up in prison. He loses both his wife ''and'' his girlfriend...but he does become his cellmate's prison bitch. (With a coffee mug that has "World's Best Bottom" scrawled on it.)
* On ''Series/{{Scandal}}'' we find out that Olivia Pope used to be the President's Press Secretary as well as his mistress. Millie, the President's wife, knew about it and was generally fine with it since the marriage was purely a political one at this point. The people who knew assumed that when the President's term in office was over he would divorce Millie and marry Olivia. However, Olivia threw a wrench into the arrangement by breaking off the relationship and quitting her job. Throughout the series the President tries to rekindle the relationship but Olivia is tired of the lies and betrayals. In season 2 the relationship between them turns outright toxic.
** One of Olivia's clients turns out to be a male example of this. He is in love with his brother's wife and they have been having a clandestine relationship for more than a decade. Olivia gives him a TheReasonYouSuckSpeech where she explains why such an arrangement is not a real relationship and he needs to end it if he wants to be ever truly happy. Of course she is partly talking about herself as well.
* In a rare male example, on ''Series/GameOfThrones'', Loras Tyrell fulfills this role when his lover Renly Baratheon marries his sister Margaery. Verges on an OpenSecret, if the amount of sarcastic references to the relationship is any indication.
* Hilariously, on the last season of ''Series/TheTudors'', Charles Brandon introduces his French girlfriend to people as his "official mistress".
* In ''AlloAllo'', Rene is cheating on his wife with Yvette, and cheating on both of them with Maria. Later he also cheats with Mimi, Michelle, Denise La Roche, Louise, and possibly most of the Communist Resistance. And apparently this wasn't all of them.
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[[folder:Music]]
* "Can't Let U Go" by {{Fabolous}} is about a man who is already married, and is torn between his wife and his girlfriend (and trying to keep the former from finding out about the latter). For now, he decides to secretly have his cake and eat it too, because [[FamilyUnfriendlyAesop "the entree ain't as good without something on the side]]. For her part, the mistress knows full well that her boyfriend is already married, and is apparently OK with the status quo.
* "Saving All My Love For You", by Whitney Houston, is from the mistress's [=POV=] as she laments that her paramour is being about as honest with her as he is with his wife and family.
[[/folder]]

[[folder:Theater]]
* ''Theatre/CyranoDeBergerac'': [[{{Villains}} De Guiche]] wants to bully heroine Roxane into this. She will have none of it.
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[[folder:Videogames]]
* King's Mistress is one of the endings in some of the ''PrincessMaker'' games.
** Not only that, the second game as a possible ending with the girl as the lover of a local landlord as well. Said landlord [[ChekhovsGun can potentially show up earlier]] and makie the girl his lover if she has high Charisma with low Morals -- it's not reccomended to just let her be, though, as her stats and overall rep will go lower.
** In said second game the King of the Land also has a royal concubine, and your daughter can speak to her. She seems to be a pretty but deadly bored woman rather disenchanted with the life of the court, but unwilling to leave it due to the benefits it still gives her.
* [[FireEmblemElibe Fire Emblem Blazing Sword]]: King Desmond of Bern has a son (Zephiel) by the queen (Helenne), and a daughter (Guinevere) by his [[NoNameGiven unnamed]] mistress. His illegitimate family lives in the palace, while his official one lives in an old out-of-the way manor. It's explained in the prequel ''Sword of Seals'' that [[spoiler: said mistress was actually the King's old girlfriend, whom the King couldn't marry due to being forced in an ArrangedMarriage with the Queen..]] Needless to say, [[BigScrewedUpFamily it does NOT end well.]]
* In ''VideoGame/DragonAgeOrigins'', [[spoiler:if you make Alistair king and cannot/will not make yourself queen and are in a romance, and provided you "hardened" him earlier, you may become his mistress. Not just a mistress, though, you may be his adviser, as well.]]
* In ''VideoGame/TalesOfSymphonia'', Zelo's father had a mistress, who was the mother of Zelo's half-sister Seles. Despite him being the Chosen, it's implied that it was something everyone knew, as Zelos and Seles not only knew about each other, but they got on rather well. The mistress wasn't happy with the arrangement though, knowing that Zelos would be TheChosenOne instead of their daughter. [[TearJerker Let's just say]] things got worse and [[DarkAndTroubledPast leave it at that.]]
[[/folder]]

[[folder:Visual Novels]]
* In ''VisualNovel/UminekoWhenTheyCry'', several characters theorize early on that the basis of the legends of Beatrice, the mysterious witch that Kinzo Ushiromiya seems to be obsessed with, is that Kinzo had a secret mistress (though Natsuhi, trying to be the loyal daughter-in-law, repeatedly tries to deny it). It turns out that [[spoiler:they're right. Kinzo did have a mistress, Beatrice Castiglioni, who he met during the second World War. They fell deeply in love, and after Kinzo bought the island of Rokkenjima he built her a secret mansion, Kuwadorian, for her to live in, and he would often visit her under the pretense that he was going on business trips. They even had a daughter, but unfortunately Beatrice [[DeathByChildbirth died in childbirth]]...and this caused Kinzo to go insane with grief, and as their daughter grew older he convinced himself that she was his mistress reincarnated, [[ParentalIncest eventually leading him to rape her and get her pregnant]].]]
[[/folder]]

[[folder:Western Animation]]
* Nurse Bendy, to Principal Fakey on ''WesternAnimation/MoralOrel''. She's pretty nonchalant about it. [[spoiler: Though the episode Alone, implies that her mental state has regressed to that of a child, and that sleeping around has made her affection starved and depressed.]]
* There's a GenderFlip on ''WesternAnimation/KingOfTheHill''. There is an OpenSecret that Nancy has been having a 14 year affair with John Redcorn. Her husband Dale and son Joseph (who happens to look exactly like John, a brown-skinned Native American) are completely oblivious.
[[/folder]]

[[folder:Real Life]]
* [[http://en.wikipedia.org/wiki/Madame_de_Pompadour Madame de Pompadour]], was one of the [[http://static.tvtropes.org/pmwiki/pub/images/Pompadour.jpg mistresses]] of [[UsefulNotes/LEtatCestMoi Louis XV]]. She was featured in ''LeChevalierDEon''. She also appeared in the ''Series/DoctorWho'' episode "The Girl In The Fireplace" (the Doctor even mentions that she and the queen were good friends).
---> '''The Doctor''': "France! It's another planet!"
** Queen Marie Leszczyńska wasn't happy with her husband's affairs at all, since she was a devout Catholic. She merely preferred the well-behaved and properly deferential Pompadour over her downright arrogant predecessors. Marie Therese, Louis XIV's Queen, on the other hand, was openly dissappointed when her husband exchanged Louise de la Valliere for de Montespan.
** Madame [=DuBarry=] was another mistress late in his life, who was an [[HistoricalVillainUpgrade initial antagonist]] in ''Anime/RoseOfVersailles''.
* Looking through the history of any European country, the amount of mistresses the royalty and nobility kept on hand is staggering. Special mention to UsefulNotes/LouisXIV, who was still sleeping around at 70, and [[http://en.wikipedia.org/wiki/Augustus_II Augustus II of Poland]], who ended up with ''350 '' children, of which ''one'' was legitimate.
* UsefulNotes/HenryVIII had two confirmed mistresses, Elizabeth Blount and Mary Boleyn (yes, sister to Anne Boleyn). He ''may'' have had other mistresses and considering his personality that wouldn't be surprising but beyond Elizabeth and Mary it is purely speculation.
** Of course, Anne herself was his quasi-mistress while he went through that whole "divorcing Catherine of Aragon" debacle.
*** Henry was a fan of marrying the mistress. Jane Seymour was his mistress (in the same, not-so-fully-consummated way that Anne had been) while he was married to Anne Boleyn, and went on to become his third wife. Catherine Howard, wife number five, was his mistress while he was married to Anne of Cleves.
* The most famous example of a queen openly keeping lovers is UsefulNotes/CatherineTheGreat. She also rewarded her lovers handsomely (one of them briefly became king of Poland). Notably she started ''before'' she had her husband overthrown (and possibly murdered) and kept it up afterward. (This is the likely point of the rumor that she died, um...'a horse' -- it was a joke about her insatiable appetite and her penchant for picking her lovers from her horse guards.)
* A Swedish example: Frederik I's mistress Hedvig Taube who (like many others) acquired a large fortune from her liaison with the king.
* [[TheHouseOfStuart King Charles II of England, Scotland, and Ireland]] was known as "the Merry Monarch" for his free-living lifestyle, and is famous for having twelve acknowledged illegitimate children by seven mistresses -- with no less than five of the children being by Barbara Palmer, Countess of Castlemaine -- and no children at all by his legitimate wife, Catherine of Braganza. Many of Charles' bastards have prominent descendants, with one of them (Diana Spencer) marrying the Prince of Wales (making Princess Di), and thus probably finally getting one of Charles' descendants in line for the throne.
** A common story is that several people started throwing insults and[=/=]or rocks at the carriage they thought contained his [[http://en.wikipedia.org/wiki/Louise_de_K%C3%A9rouaille,_Duchess_of_Portsmouth French-born Mistress]] until [[http://en.wikipedia.org/wiki/Nell_Gwyn Nell Gwyn]] leaned out the window and noted with a smile:
---> "Good people, you are mistaken; I am the ''Protestant'' whore."
* [[TheHouseOfHanover William IV of the United Kingdom]] was also famous for a large number of illegitimate children (as, frankly, were many of the sons of George III, much to their devout and HappilyMarried father's disgust--at least when he was lucid enough to be disgusted). He had only two daughters by his wife, Adelaide of Saxe-Meiningen, but he had ten by his mistress, the actress Dorothea Jordan. Both of his legitimate daughters died, leaving the throne to his niece [[UsefulNotes/QueenVictoria Victoria]]. And of course, William's surviving children had important descendants, the most famous of whom is current [[UsefulNotes/TheMenOfDowningStreet Prime Minister]] UsefulNotes/DavidCameron.
** William's case was a bit different, though, in that all of his bastards were born before his marriage, he dumped his mistress long before marrying, and his marriage was actually [[HappilyMarried quite happy]].
** Of course, marrying their mistresses wasn't much of an option to the children of George III, despite several attempts to try. They had to have the permission of the monarch (for most of their lives, their father) to marry, which wasn't granted. One son - Prince Augustus Frederick, Duke of Sussex, had two marriages declared invalid because his father hadn't given him permission.
* MarionDavies, longtime girlfriend of publishing magnate Creator/WilliamRandolphHearst. Hearst remained married to his wife Millicent until his death, despite having been carrying on with Davies for the last 34 years.
* Edward IV seems to have slept with something like half the married noblewomen in England. Interestingly, this seems to have helped him politically, as his mistresses would influence their husbands to support him in the War of the Roses.
[[/folder]]

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