Say your wife dies all of a sudden, leaving you a widower, and especially if you have children this can leave them without a mother.
Well, if you've been carrying on an illicit affair on the side, just marry your mistress and problem solved! No need to go into the dating scene again when there's someone you already have a relationship with waiting in the wings.
Naturally, this is usually seen as quite scandalous, especially if the affair was only rumored and the quick turnaround on remarrying just seems to confirm what everyone already suspected. Even more so if the new bride is already pregnant which leaves no doubt as to what was going on. The level of sympathy the characters involved are expected to receive from the audience depends heavily on where the story falls on the Good Adultery, Bad Adultery scale. More sympathetic examples frequently have the first spouse being unwanted and have the marriage not be totally willing, usually through an Arranged Marriage, in which case the relationship with the mistress might have already existed and the two would have married first if they'd been able to. However, if everyone was aware of what was going on from the beginning and the only reason both relationships weren't legally recognized was because of the laws in the setting and/or to avoid a public scandal, it's Polyamory, and the remarriage to the mistress is usually not played as a negative, especially if she already has a positive relationship with any existing children. Sometimes the first wife even encouraged the two to marry if anything happened to her, often for the children's sake so they can grow up with a mother.
Often the Gender-Inverted Trope to the Cuckold. In societies where husbands held all, or most, marital rights and privileges, it was considered a sign of weakness to suffer his wife having an affair. On the other hand, a husband cheating would be justified on the grounds of I'm a Man; I Can't Help It. Thus, the Double Standard was that a woman having an affair was an insult, but a man having an affair was just "natural" unless this trope came into play, and she was at risk of being replaced. It is possible for this trope to be gender-inverted with a woman marrying a man she's been seeing on the side, but it's considerably rarer.
The mistress also has a high chance of being a Wicked Stepmother to any children from the first marriage. If the mistress already comes with children fathered by her new husband, it's Secret Other Family, and in some cases, she might not have even known her lover had a legal wife, in which case she's just as likely to be portrayed as a victim to a serial liar. This is nearly guaranteed to get you Parental Issues up the wazoo and make a Parent with New Paramour situation even more awkward.
If the first spouse was gotten out of the way specifically so this could happen it overlaps with Murder the Hypotenuse, especially since Divorce Requires Death and this may be seen as the only way the two can be together. Laser-Guided Karma may strike the mistress if she arranged or was complicit in the death of the first wife and later finds herself being cheated on and eventually replaced. If a man does this serially and is the one killing his wives you're likely dealing with The Bluebeard.
- Asuka's father in Neon Genesis Evangelion began having an affair soon after his wife Kyoko lost her mind during the Eva contact experiment, and everyone (including Asuka) knew about the relationship, which was with Kyoko's own doctor. After Kyoko killed herself (which is implied to have been at least in part to spurn her husband) he married the doctor, and while Asuka makes it clear she doesn't loathe the lady she also doesn't particularly like her and only keeps up a facade of being friendly with her on the phone.
- In the backstory of Tenchi Muyo! Prince Yosho combines this with New Old Flame. As a young man he had a Secret Relationship with a fellow student named Airi (while engaged to his half-sister Ayeka) while both were at the Galaxy Police Academy, but after he ran away and ended up on Earth he eventually married another woman named Kasumi and started a family. After Kasumi inevitably died before him due to his Jurain blood he laid low for several years until Airi reappeared and revealed that she had actually been pregnant with his child and since she was also engaged at the time she ended up breaking it off prior to giving birth. She then introduces him to their daughter Minaho, and Yosho and Airi got back together and became common law married, having another daughter, Kiyone, who was Tenchi's mother. They're both portrayed sympathetically since neither of their engagements was their own choice, and when Ayeka reappears and turns out to have been looking for him all this time it's evident that he's surprised she's still carrying a torch for him since he never actually took their engagement seriously and, unlike her, realized it was purely to silence those who objected to his mostly human heritage.
- In Heat Guy J, Kia talks about how his father, a musician named Blues Dullia (an Expy of John Lennon) spent years abusing his wife and cheating on her, then finally ditched her when he found out his mistress was pregnant and started a new life with her. Shortly afterwards, Kia's mother passed away, making this a sort of inversion of the trope: the second marriage happened before the death of Mr. Dullia's first wife. Kia went to inform his father of his mother's death, but couldn't bring himself to do it when he saw his dad playing with the child from that union. It's unknown where Kia went after that, or who (if anybody) was taking care of him.
- James Gordon in Batman eventually got remarried to Detective Sarah Essen, with whom he was having an affair in Batman: Year One when the two were working together but broke off after it was discovered and she moved to Chicago for several years until they reunited. In a variation, Gordon's first wife was still alive but had divorced him, and Jim's daughter Barbara actually liked her new stepmother with no apparent ill feelings, and after Sarah's death in Batman: No Man's Land, Barbara was sad that she never got around to calling Sarah Mom.
- After Cyclops lost Jean Grey in New X-Men he eventually gets together with Emma Frost, with whom he had been having a Mental Affair when Emma was his therapist. In a twist Jean herself was shown to have psychically pushed the two together from beyond the grave, which didn't sit well with many fans. Emma and Scott eventually broke up in Avengers vs. X-Men with the one-two punch of Emma revealing her affair with Namor and Scott choking her to gain her part of the Phoenix Force.
- In The Duchess, The Duke ends up doing this with his mistress Bess Foster after his wife Georgiana dies at the end of the movie. When she first found out about the affair Georgiana was not happy with either of them, especially since Bess was previously her best friend, but she comes to realize that Bess only had the affair (initially) to regain her children, something she herself experiences later once her own affair with Charles Grey is discovered and she's blackmailed into ending it under the threat of never seeing her illegitimate daughter with Grey again. In the end, Georgiana gives the two her blessing to remarry when she knows she is going to die, while never truly forgiving her husband for his actions. The movie as a whole is an exploration of the Double Standard around a husband's affair versus a wife's.
- Shows up in some Agatha Christie stories, with two variations in The Twelve Tasks Of Hercule Poirot:
- The Nemean Lion: Poirot tells a rich businessman (whose shrewish wife hired him to find her lapdog) about a case he knew about years ago, where a man poisoned his wife's coffee every day so he'd be free to marry his secretary. The tycoon takes the hint and his wife's mood improves considerably after her morning coffee starts tasting better.
- The Lernean Hydra: A doctor admits that after his wife died, he'd have proposed to his assistant if it weren't for this trope (the theme of this particular story is the power of rumors). When an investigation (by public demand) reveals the wife was poisoned, Poirot finds out the murderer was actually a nurse, who thought the doctor would fall for her instead (and caused the investigation in retaliation).
- Gender-inverted in the Arcia Chronicles, when Duchess Martha Tagere marries her long-time lover Cesar Malvani after her husband, the Duke of Orgonda, is murdered by the mob.
- In A Song of Ice and Fire, King Maegor The Cruel of the Targaryen dynasty, in a direct reference to Henry VIII, had a total of six wives. In particular, Queen Tyanna of the Tower was formerly his Pentoshi mistress before marrying him in the wake of his second wife, Alys Harroway, being executed for (alleged) adultery that resulted in stillborn and deformed children. When Maegor found out that Tyanna had lied about the adultery to get Alys killed, and was the real cause of the stillborn children due to giving Alys poison, he had Tyanna herself executed as well.
- It also turns out that in a gender-flipped example Jon Arryn's death was a case of Til Murder Do Us Part, with the current spouse Lysa Arryn plotting the death of her husband and then marrying Petyr Baelish, with whom she had been having an affair on the side. Baelish eventually offs her as well once she's no longer of any use to him.
- In the book Lives of the Monster Dogs Augustus Rank's father married his mistress soon after his first wife and Augustus's mother passed away, in the process revealing he had a son with his mistress, Augustus's half-brother, who would eventually be killed by him over the affections of a woman both men loved.
- This was part of Lord Soth's Slowly Slipping Into Evil in the Dragonlance series. While still married to his first wife Korrine, he and his band of warriors rescued a band of elven priestesses and he instantly fell in love with one of them, Isolde, and began having an affair with her on the side. When Korrine, who had gone to a witch to help them conceive a child (whom the witch warned would represent Soth's soul) gave birth to an abomination, Soth killed her and the child because he thought she had been cheating on him with a demon, and covered it up to make it look like she and the baby had suffered Death by Childbirth instead. Eventually, the truth came out and Soth was exposed before the court, and he ran away before he could be punished and got remarried to Isolde, who had also been pregnant with his bastard child at the time Korrine died and eventually gave birth to a healthy child. But then as he was setting off to prevent The Cataclysm yet again Soth was convinced his wife was cheating on him (by the same three elven maidens who had ratted him out on the truth about his first wife, no less) and trying to pull The Uriah Gambit on him. He then went to confront her, and because he had been distracted from his quest, The Cataclysm started and a chandelier fell on Isolde and the child as the entire castle began to come down. He chose not to save them and Isolde cursed him with her last breath, which caused him to rise again as Death Knight.
- In I, Claudius the relationship between Livia and Emperor Augustus is described this way. Once they're actually married, Augustus ends up being unable to perform sexually with her out of guilt at having stolen her from her first husband, so she arranges for him to have mistresses on the side since the entire marriage is a power play in the first place.
- In the novel version of The Manchurian Candidate, where Raymond Shaw's mother was having an affair with John Iselin while still married to Raymond's father, and eventually divorced him to marry Iselin when she became pregnant with Raymond's half-brother. The passage describing this, incidentally, was eventually discovered to have been plagiarized almost word-for-word from I Claudius above, including the bits about the wife arranging for other women to satisfy him when he couldn't perform out of guilt.
- In Jennifer Roberson's Chronicles of the Cheysuli, Niall has his insane wife Gisella sent away and lives openly with his mistress Deirdre; when he receives word that Gisella has died, he marries Deirdre even though he himself is on his deathbed.
- Seen in Nerilka's Story, a side novella of the Dragonriders of Pern series which takes place during and after the events of Moreta: Dragonlady of Pern. Nerilka's father is one of the Lord Holders of Pern, and after he loses his wife (Nerilka's mother) to the plague which besets Pern for a time, he almost immediately moves his mistress in to take her place — along with her entire family. Nerilka is not pleased and makes a point of removing her mother's personal effects from her rooms before her new stepmother can arrive and claim them for herself.
- In an episode of The Outer Limits (1995), a time traveler goes back in time to the last-19th century Austria and becomes the live-in nanny for little Adolf Hitler (planning to kill him). She discovers that the maid is having an affair with her employer, Adolf's father, while his wife is sick in another bedroom. She tells the maid that the man is simply having fun with her and will never follow through on his promise to marry her. The maid counters that the current Frau Hitler used to be the maid as well.
- The Handmaid's Tale: Luke Bankhole had an extra-marital relationship with the main protagonist June Osborne. He left his old wife to marry June and had a new family with her. It's for this reason that when the Gilead regime is established, June is considered an "adulteress" for leading another man astray and is turned into a Handmaid.
- In Crusader Kings II this can be easily done by a ruler who used the Seduction focus to run around on his or her spouse, and even recommended because the +40 to your spouse's opinion for being your lover means they're both less likely to support plots to kill you and more likely to produce children. The only thing to be careful of is that marrying a character of low rank costs the ruler Prestige.
- As revealed in Dragon Age: Origins's DLC "Return To Ostagar", King Cailan of Fereldan planned on doing this before he was killed with Celene, the Empress of Orlais, using his wife Anora's alleged infertility as cause to divorce her. You find this out through letters in Cailan's tent, and if Anora's father, Loghain, is with the party at the time, he minces no words at the two of them. Curiously, later games and novels reveal that if such a union happened, it would have been purely political since Celene isn't into men, but she exchanged romantic letters in an attempt to secure hold over Ferelden.
- The more benign version is all but stated to have occurred in Fire Emblem Fates with King Sumeragi, who was married to Queen Ikona, the mother of his children, at the time he met The Avatar's mother Mikoto, fell in Love at First Sight with her began a relationship with her (possibly taking her as a concubine, a well known practice among Japanese royalty from the Heian to the Meiji era). When Ikona died some years later, Sumeragi eventually married Mikoto; she became the stepmother of his children by Ikona and finished raising them after Sumeragi's death and the Avatar's kidnapping. There's no apparent angst on the part of anyone involved (aside of Princess Hinoka saying that she had early objections with the arrangement, but eventually came around and regrets her early behavior), suggesting it was the "everyone knew about it and was fine with it" variant of this trope, and Mikoto is beloved by her stepchildren, her ward and niece Azura, and by everyone in the kingdom.
- When They Cry:
- In a version without the spouse actually dying, plus a Gender Flip, in Higurashi: When They Cry Rena's mother divorced her father and married her boyfriend, a coworker, because she was pregnant by the boyfriend. This devastated Rena, in part because she actually liked the boyfriend before this happened, not knowing the nature of his relationship with her mother.
- Rudolf Uroshimiya earned the ire of his son Battler in Umineko: When They Cry by marrying his business partner and lover Kyrie way too soon after his wife Asumu died, causing Battler to move out and live with his maternal grandparents for several years. For worse, Kyrie was already pregnant with Battler's sister Ange when she married Rudolf, showing that even after Rudolf married Asumu he never actually ended the relationship with Kyrie. Despite this Battler actually likes Kyrie, seeing her as a Cool Big Sis, and directs all his anger at his father for his behavior (and it's indicated that Rudolf is still seeing other women even after marrying Kyrie). Kyrie also reveals late in the game that if Asumu hadn't died on her own she would have killed her to be with Rudolf.
- In Better Days this happens twice:
- A time-delayed version where Fisk and Lucy's mother Sheila has an affair with her married next-door neighbor Sam, who was also the father of Fisk's best friend, and after this is discovered Sam's marriage crumbles as a result (and was already on shaky footing due to his wife's paranoia which pushed him into the affair in the first place). The two eventually get married when Fisk and Lucy become adults so it's not quite as sudden as most examples, but still counts.
- Elizabeth catches her husband cheating on her with the head of their homeowner's association and begins a relationship with Fisk, who she had feelings for years ago but had moved on from, and eventually divorces her husband and marries Fisk, starting a family as seen in Original Life.
- In Blindsprings, Asher Thorne is implied to have done this, since Word of God says that in the events leading to him arresting and imprisoning his first wife for teaching their daughters about their Orphic heritage he brought other people into the marriage, and after arresting her divorced his first wife and married Giselle, who's implied to have been his mistress. Giselle is definitely the Wicked Stepmother variety and makes her disdain for Asher's first family quite clear.
- Henry VIII did this several times, even splitting from the Catholic Church so he could marry Anne Boleyn and divorce his first wife Catherine of Aragon. Most of his other wives were also his mistress at some point as well.
- The relationship between Prince Charles and Camilla Parker Bowles is often simplified as being this, but in reality was a bit more complicated. Charles and Camilla had a relationship in the 70s but for various and conflicting reasons (depending on who you ask) officially broke up but remained lovers in secret, even after Charles eventually married Diana and Camilla married Andrew Parker Bowles. Eventually both marriages ended in divorce and the two of them resumed their public relationship after this. Charles and Camilla only officially married in 2005, while Diana died in 1997.
- Though he didn't get far enough to actually do the remarrying part, Hawley Harvey Crippen killed his wife Cora in London in 1910 and covered it up by saying she had left him to live with family in America. After people began asking questions he went so far as to forge letters saying Cora had died in America, presumably so he could then legally marry his secretary/lover Ethel. Once people began to doubt this story he chose to flee to Canada with Ethel and planned on establishing a new identity and marrying her once they got there. However they were spotted on the boat taking them to Canada (and for some reason Ethel was dressed as a young boy and pretending to be Crippen's son, a disguise that fooled precisely no one) and the boat's crew used the newly invented telegraph to warn Scotland Yard of their presence, allowing the two to be arrested on the other side of the Atlantic as soon as the boat landed. The extent of Ethel's involvement in Cora's death has never been conclusively proven and she was acquitted at trial due to lack of evidence, but it's believed she at least knew Cora was dead as she was seen wearing her furs in public and for all intents and purposes took over in the role of a wife after Cora's disappearance.
- Theodor Geisel (a.k.a. Dr. Seuss) had an affair with Audrey Stone Dimond after forty years of marriage to his then-wife Helen Palmer. Distraught over this and a series of health problems in her life, Helen committed suicide in 1967. Geisel married his mistress just eight months later, and they remained married until his death in 1991.
- Drew Peterson, who was eventually tried and convicted for the murder of Kathleen Savio, serially did this, having been married 4 times and cheating on the second wife with Kathleen, who would eventually become wife #3, and then cheating on her with Stacy Peterson, who became wife #4 and whose body has never been found but is believed to have been killed by him as well, making him a classic example of The Bluebeard.
- A couple examples from Ancient Rome:
- Caligula's fourth and final wife Milonia Caesonia was his mistress while he was still married to his third, Lollia Paulina, and Caesonia gave birth to her and Caligula's daughter Julia on or soon after their wedding day after he divorced Paulina after only six months of marriage for allegedly being infertile. His hasty marriage to Caesonia was mostly to make sure that Julia would be born legitimate and be able to become his heir, and it's speculated that Caligula's desire for an heir might be why he got together with Caesonia in the first place, since she already had 3 daughters and thus proven fertility.
- Caligula's nephew Nero had a mistress in Poppaea Sabina while married to his first wife Claudia Octavia, and after divorcing her using (probably false) claims of adultery married Poppaea, who was already pregnant with his child at the time. Poppaea herself died a few years later either in Death by Childbirth (most likely) or at the hands of Nero when he kicked her in the stomach in a fit of rage (if you believe certain biased historians) but by all accounts he was genuinely fond of her and took a shining to a male slave named Sporus who resembled her, going so far as to have him castrated to serve as a wife and was known to refer to him by her name. His third wife Statilia Messalina was also his mistress prior to marrying him, though she actually survived him.
- Sir James Goldsmith admitted that despite it often being attributed to him the page quote was actually first stated by Sacha Guitry, but Goldsmith definitely practiced this. His third wife Lady Annabel Goldsmith was previously his mistress, and the two married solely to legitimize the two children they'd had while he was still married to his second wife. And after that relationship ended Goldsmith referred to Laure Boulay de La Meurthe, his mistress while he was married to Annabel, as his wife despite the fact that the two never formally married, since for all intents and purposes she was until his death.
- John of Gaunt, father of Henry IV of England, married his long-time mistress Katherine Swynford after the death of his second wife, and had their children declared officially legitimate. It was a bit of a scandal, because of the adulterous relationship and, moreso, the fact that Katherine's family were minor gentry. When Henry IV became king of England in 1399, he barred his half-siblings and their descendants from the line of succession, but one of them eventually ascended the throne in 1485 as Henry VII.
- Averted by a much later British king, George II. He had mistresses while married to his wife, but she knew, and personally approved each one - they were actually Happily Married and quite devoted to each other. On her deathbed she asked him to remarry, and he famously said, "Non, j'aurai des maitresses!" (No, I will have mistresses! - French was, in those days, commonly spoken among the aristocracy and royalty of Europe.) He never remarried.