Oops, I Forgot I Was Married

"See that girl/ With the diamond ring?

She knows how to/ Shake that thing!

Aww, mess around

I declare she can mess around

Ray Charles, "Mess Around""

Sometimes when a writer is looking to stir things up, or prevent the inevitable progression of a relationship, or stop a wedding, we'll find out that oops, once upon a time our hero/ine had an Accidental Marriage, Arranged Marriage or Citizenship Marriage, possibly brought on by an Off the Wagon night. Which they then proceeded to forget about for years on end until their long-lost spouse comes looking for them wanting a divorce, or they want to marry their current SO. Occasionally they'll think the marriage was annulled or never really counted, or they'll foolishly trust their spouse to take care of doing away with the ill-advised nuptials. It can be a bit more forgivable if the returning spouse supposedly died.

Depending on the situation, this can result in a New Old Flame starting a Love Triangle, a very much unwanted Stalker With a Crush, or a second chance at a missed opportunity.

This is somewhat uncommon in Real Life, but not unheard of - some people really can't be bothered with the paperwork necessary to get a proper annulment/divorce for a relationship that's long since over. However, the New Old Flame complication generally only happens in Real Life in cases of intentional bigamy.

Can happen with The Mistress.

Advertising

 * Currently there is T-Mobile commercial that commits this trope. Catherine Zeta-Jones is sitting in a living room discussing plans with a T-Mobile customer. Said customer is male and stares at Jones in an uncomfortably awkward fashion while his wife is SITTING RIGHT NEXT TO HER. He then makes the remark, "This is my wife. We're married...technically." What kept the wife from leaping across the room and strangling the bastard is beyond any laws of reason.

Film

 * The Accidental Husband Starring Uma Thurman. In this case, the title is sort of misleading: Thurman plays a relationship talk show host who advises one of her listeners to break up with her boyfriend. When said boyfriend learns the host is about to get married, he gets his revenge by having a kid hack into a government database and list her as married to him. "Hilarity" Ensues.
 * Bill and Jo in Twister. Bill and Jo had long split up, but never signed the divorce papers until Bill shows up with his new fiancee. It makes one wonder exactly how and when Bill broke the news to her. First date? Second date? The marriage proposal? "Honey will you marry me?" "Yes!" "Great! Would you mind coming along on a road trip to visit my current wife so she and I can get divorced?" "What?!"
 * Sweet Home Alabama has the main plot ride on one of these, as the main character not only never got divorced, but even leads her new fiance to believe her first husband was her cousin. And it takes place in the deep south...
 * Move Over Darling (Doris Day, James Garner, and Polly Bergen)is a 1963 remake of a1940 screwball comedy My Favorite Wife (Irene Dunne, Cary Grant and Randolph Scott). The plot is: a wife was lost off a ship that sunk. Presumed dead after 7 years, the husband remarries. However, the first wife has been living on a deserted island with another man, is rescued, and comes home on the wedding day.

Literature

 * Mr. Rochester in Jane Eyre.
 * Sissy in A Tree Grows in Brooklyn.
 * Barbara in Harry Turtledove's World War series. Her husband Jens went missing during a scouting mission and was assumed KIA. By the time he caught up with her, she was already remarried and pregnant, driving him to a Face Heel Turn.
 * The first husband of Hatty Doran in the Sherlock Holmes story "The Adventure of the Noble Bachelor" was reported killed in an Apache raid on his mining camp. She only learns that he didn't die when she sees him at her second wedding.
 * In Animorphs, Marco's dad remarries a few years after his first wife "died." Unknown to him, his wife was still alive--she was the host of Visser One, who Faked The Dead when it was time to leave the planet. Needless to say this situation was quite awkward for Marco, who knew his mom was alive but couldn't tell anyone.

Live Action TV
"Lilith: "Oh look, it's my first husband.""
 * Phoebe from Friends is very fond of this trope. She married a Not-So-Gay Ice Dancer and conveniently forgot to mention it to even her best friends and it is implied that she also married an unknown (to the viewers) man in Las Vegas.
 * Also from Friends, Rachel trusts Ross to annul their drunken Vegas marriage - and he doesn't go through with it.
 * Angela on Bones
 * Sam on Burn Notice drifted apart from his wife and eventually lost contact with her altogether. He never bothered to file for divorce because he thought, as a womanizing spy, that he wouldn't live long enough to settle down. Several decades later, his girlfriend proposes...
 * Gus on Psych
 * His best man was a goat since the whole wedding party was pretty drunk at the time. Shawn is pissed because he was supposed to be that goat!
 * Mr. McQueen on Popular
 * Sheridan on Babylon 5. Twice. Though in all fairness, he did divorce the first one long before the series began, and the second one was presumed dead. And what did come back was little more than a Shadow meat-puppet. Later, Sheridan enacted a more thorough dissolution of their marriage,
 * First one was legally divorced VERY quickly, and actually averted this trope by never being a problem.
 * Also he never hid his marriage to Anna, which was happy until her (presumed) death, so it doesn't completely count.
 * G.O.B. on Arrested Development, explained as the logical conclusion to a series of drunken dares with a woman (played by Will Arnett's actual wife Amy Poehler) he met at a bar. The sad thing: he could have gotten it annulled if he'd just admit that he never actually had sex with the woman.
 * Mimi on The Drew Carey Show. She was married to Eddie Money for a week.
 * In that case, she'd been divorced; the problem was that the church she wanted to be married in refused to do the ceremony unless she got an annulment.
 * On Angel, Doyle was married to some woman, which he neglected to tell Cordelia. Said woman came looking for a divorce as she found a new husband.
 * Edward and the mistake he and Kitty swore never to talk about in Dharma and Greg. He trusted her to file the paperwork, and she... forgot. The problem is never resolved, because it turns Kitty on that she's "the other woman", effectively un-probleming it.
 * Karen Darling from Dirty Sexy Money.
 * Frasier Crane was married prior to him appearing on Cheers, to fellow medical student Nanette Guzman. They were only married for a few months and then divorced. Years later, when Frasier was married to Lilith, Nanette reappeared as a children's entertainer called "Nanny Gee". Turns out Frasier never told Lilith about his first marriage, leading to a conflict between The Missus and The Ex.

"Earl: "Oh, my God! You're married?!"
 * Nanette later appeared in an episode of Frasier, and she tried to seduce Frasier despite having remarried herself. (Incidentally, Nanette was also an example of The Other Darrin, being played by Emma Thompson in the Cheers episode and by Laurie Metcalf in the Frasier one.
 * Sarah 'Mac' Mackenzie on JAG especially Egregious in that she is a lawyer and US Marine officer.
 * 3rd Rock From the Sun has a fascinating twist on this. As just when Dick Solomon is about to get married The Big Giant Head decides to send a wife to him. Thus he didn't 'forget' he was married, but was suddenly forced to ret-con a wife into his life, and yes, hilarity ensues.
 * On Wings, Helen was about to marry Joe but she forgot to divorce Antonio who she married for citizenship reasons.
 * On Scrubs Dr. Cox and Jordan find out that they never correctly filed their divorce and so are legally still married. Being the weird couple they are, this actually ruins their sex life and puts serious strain on their relationship. At the end of the episode, Cox gets down on one knee and asks Jordan to divorce him again. They go back to being a happy, independent, royally screwed up couple after they file the paper work.
 * Though not married, Craig did pull this in Degrassi when he was having an affair. Manny didn't want to be Craig's skank on the side, and he told her that he broke up with Ashley so that they can be together. The problem is he doesn't break up with her, and now is cheating on both girls with eachother. Leading to both finding out and dumping him on the spot.
 * On Shameless (US) Kevin proposes to Veronica while drunk. It takes a while for him to confess to her that he never divorced his first wife. According to him she was a total psycho and he is actually in hiding from her. If he asks her for a divorce now, he fears she will kill him. Veronica is actually fine with this and  just so they don't disappoint Veronica's mother and more importantly get wedding gifts.
 * Inverted on The Dick Van Dyke Show where Rob and Laura discovered they're not actually married because Laura had lied about her age in order to marry (she was 17 apparently). They fix it by quickly getting married ... again.
 * On My Name Is Earl, Joy tricks Earl into marrying her, by getting her friends to serve him "upside-down martinis", before driving off to Las Vegas with him. The next morning, Earl wakes up badly hungover, and spots Joy's wedding ring.

Joy: "Yeah, sweetie. To you!"

Earl: Beat "'Scuse me." Vomit Discretion Shot"

Mythology

 * Medea in Jason and the Argonauts and their Quest for the Golden Fleece. At first, Medea helps him complete the insanely difficult tasks her father sets him provided he marries her. After embarking on adventure and obtaining said Golden Fleece, they eventually arrive in Corinth, where Jason engages himself to the daughter of the king. Medea was not happy. Makes this trope. Older Than Feudalism.

Professional Wrestling

 * In the old-school WWF: during her on screen marriage to Triple H, Stephanie McMahon was drunk enough not to remember about it anything until the groom made the announcement at her wedding to Test. Incidentally McMahon and Triple H later got married in real life (the bride was sober then).

Webcomics

 * Trace in Two Kinds, having amnesia, fully forgets that he was married. His wife, Saria, does not.
 * from Juvenile Diversion not only forgot his wedding along with his name, but . Needless to say, his wife was not pleased.

Western Animation

 * The Simpsons had an episode where Homer and Flanders' "Vegas wives" - two cocktail waitresses they had accidentally married several seasons earlier during a drunken bender at Caesar's Palace - reappeared long after they (and the viewers) had forgotten about them. The local judge ruled that polygamy, or "Mormon Hold-Em" was legal in Nevada and therefore Homer and Ned had to support both wives.
 * Well, Homer did. Ned's "real" wife had died by this point, so he just had to try to be a good husband to his new one. (Un)fortunately, she quickly grew tired of his squeaky-clean lifestyle and ran for the hills.
 * Also of note: Homer got rid of his Vegas wife by, which apparently works like an automatic annulment in whatever state Springfield is in.
 * Done hilariously on Camp Lazlo. One season ended with Jane, the love of Lumpus' life, getting engaged to the next guy who walked up: some old man. A season later, they almost got married---but in the middle of the wedding, his other three wives complained. His excuse? Senility.

Real Life

 * This may come up with one's religious practices. For example, a Catholic may get legally divorced, but may discover years later that they need to qualify for an annulment to remarry in the Church. Traditional Jews have similar practices; there is even a specific term, agunah, for a woman whose husband has not yet divorced her, however long they have been apart.
 * May be a borderline case, but in his Psychopathology of Everyday Life, Sigmund Freud related an anecdote of a recently-married woman who was walking around Vienna with a friend of hers, and pointed to a man across the street, saying, "Look, there's Mr. X!" Mr. X, of course, was her new husband. The husband and wife had a good laugh over that story later, but Freud felt a chill when he first heard it. As he predicted, their marriage ended badly.
 * In Hamilton, Ontario, there is a section of a street called "Hess Village" - the entire run is cobbled and covered in pubs and bars. And a wedding chapel. They actually have a sign in the window saying they don't do drunk weddings.
 * The only worthwhile thing about the reality series Married by America was the discovery that one of the contestants was already married; she tried to justify going on the show by saying it was an impulsive Vegas marriage and she and the man broke up soon afterwards and never actually lived together, but the fact that neither ever bothered to annul it got her kicked off anyway.
 * While people don't tend to forget they are married without amnesia or something of the kind, it is quite common to make some mistake in filing the divorce papers, and then not finding out the divorce was invalid until one party tries to remarry.
 * During his Presidential campaign of 1828, Andrew Jackson's wife was accused of bigamy. She had separated from her first (and abusive) husband in 1790, and both she and Jackson thought she was divorced. She wasn't. They got matters straightened out in 1794, but if you think that minor detail would make any difference you don't know American politics.
 * The scandal probably contributed to Rachel Jackson's early death, as bigamy (on a woman's part, at least) was considered no better than whoredom.