Cast Incest

"Abed: When you guys first came in, we were as wholesome as the family in The Brady Bunch. Now we’re as dysfunctional and incestuous as the cast of The Brady Bunch."

- Community, "Romantic Expressionism"

Cast Incest is a variant of Romance On the Set, where two actors from a TV series or Film start dating in real world, after they've been playing family members in the show. Or maybe they were cast into a part specifically because they were already dating/married.

Sometimes it can come from a bad Actor Allusion if two people are playing a couple in a production when they had previously played family members or vice versa.

For the far squickier inversion, see Incestuous Casting.

Film

 * Ferris Buellers Day Off: On-screen siblings Matthew Broderick and Jennifer Grey dated after appearing in this film together.
 * Blades of Glory: The actors who play the brother and sister ice skating duo are married in real life, well before the film was made. And it's not exactly platonic in the film either.
 * Mrs. Miniver: Greer Garson married Richard Ney, who was her on-screen son.
 * Robert Pattinson, who plays Edward Cullen in Twilight, was seen dating his co-star Nikki Reed, who plays Rosalie Hale, his adoptive sister in the movie.
 * Made even funnier by the fact that, in the book, their characters were supposed to fall for each other but never did.
 * Nikki Reed also dated for two years Victor Rasuk who played her onscreen brother in the movie Lords of Dogtown.
 * Loverboy (not the one with Patrick Dempsey): Kevin Bacon plays his real-life wife's father. No wonder the character's screwed up.
 * The Evil Dead: Bruce Campbell revealed in a Q&A session that he lost his virginity to Ellen Sandweiss. At age 23.

Live Action TV

 * Doctor Who: David Tennant, the Tenth Doctor, is engaged to Georgia Moffett who played the eponymous character in "The Doctor's Daughter". Not only that, Georgia Moffett is the daughter of Peter Davison, one of Tennant's predecessors in the role. Georgia's marrying the man who is in her father's role as her father as her father and fathered her daughter.
 * They now have a child together, so there is now a child out there that has The Doctor as a father and a grandfather.
 * Dexter: Michael C. Hall (Dexter Morgan) and Jennifer Carpenter (Debra Morgan) are playing onscreen siblings when in real life they are married.
 * The Cast Incest isn't quite as squicky as the fact that Debra (quite unknowingly) dated her (adoptive) brother's (biological) brother.
 * Hall and Carpenter have since divorced.
 * Bizarrely
 * Everwood: Emily Van Camp ("Amy") and Chris Pratt ("Bright") dated in real life while being siblings on the series.
 * Wizards of Waverly Place's actors, Selena Gomez and David Henrie, who play brother and sister, were seen, in Puerto Rico, dining at a restaurant known by locals as a "dating hotspot". It doesn't help the fact that they seem to like each other a lot since their own characters, in the movie, appear to have UST problems, according to many fans. Selena even said in an interview that she actually had a crush on David when they were younger.
 * That was a few years ago, now they recently admitted that they use to casually date, but they don't want to get involved into something serious, due to the fact that, well, they are Justin and Alex Russo after all.
 * Ryo Narushima (formerly Keiko Hayase) and Ryuhei Kobayashi, the actors who played the twin Hoshikawa siblings of Remi and Fumiya in Chikyuu Sentai Fiveman, dated each other while filming the series. They were married after the show ended and have since raised three children.
 * Heroes: Heroes co-stars Hayden Panettiere (Claire Bennet) and Milo Ventimiglia (Peter Petrelli) dated while playing an onscreen uncle and niece. They've since broken up, but that hasn't stopped the shippers from shipping Peter/Claire who are uncle and niece.
 * Or the writers.
 * The Brady Bunch: Barry Williams (Greg) went out to dinner once with Florence Henderson, his TV (step) mom, and the media made a bigger deal out of it than it actually was. A full-fledged relationship did not come of it.
 * There was a behind-the-scenes special a few years back that revealed that just about everyone ended up hooking up to one extent or another, usually with their counterpart.
 * Due South: Paul Gross is married in real life to the actress who played his character's mother (she died young).
 * She also played his (off-and-on) lover in Slings & Arrows a few years down the road. Not only that, but much of this series, which is an employment comedy about theatre, revolves around the (dysfunctional) familyishness of said theatre.
 * Lost: Michael Emerson is married to the woman who plays Ben's mother. Somewhat offset by the fact they never share screen-time with each other.
 * Ian Somerhalder (Boone) and Maggie Grace (Shannon) briefly dated.
 * This also happened to be canon incest for the characters. I mean, they're step-siblings, but they call each other brother/sister. It's confusing and awkward.
 * Brothers and Sisters had to do a serious retcon due to the sexual chemistry between the actors playing half-siblings Rebecca and Justin. Supposedly these two dated early on in the run of the show.
 * Which is especially funny as the actress playing Rebecca, Emily Van Camp, is also mentioned in the Everwood entry above
 * On Roswell the actors who played Max and Isabel (siblings) were dating in real life.
 * David Cassidy and Susan Dey, who played siblings on The Partridge Family, slept together shortly after the series ended. She had a huge crush on him; he claimed he loved her like a sister, but made an effort anyway. It didn't work out.
 * Bruce Boxleitner married Kathryn Holcomb, his TV sister from How the West Was Won.
 * Early on in the run of Nip Tuck onscreen mother and son Joely Richardson (Julia) and John Hensley (Matt) were dating in real life.
 * The gossip sites are now reporting that Lauren Graham and Peter Krause who play siblings on Parenthood are dating.
 * Gossip sites have also reported that Sally Field, who plays family matriarch Nora Walker on the contemporary ABC drama "Brothers & Sisters", briefly dated David Annable, who plays Justin Walker, one of her sons.
 * In Strangers With Candy, Stephen Colbert's wife briefly appears as his character's mother in a flashback. To make things interesting, in The Movie, she's his character's wife (who was played by a different actress in the series).
 * In the 80s mini-series North and South (the Second Book), Kirstie Alley and her then-husband Parker Stevenson played siblings Virgilia and Billy Hazard, respectively.
 * John Travolta became romantically involved with Diana Hyland after she played his mother in The Boy in The Plastic Bubble
 * Blue Bloods: Alluded to in an interview, where Tom Selleck had to remind himself not to have any chemistry with his on-screen adult daughter.
 * Real-life married couple David and Tamela Mann play father and daughter on Tyler Perry's Meet the Browns.
 * Degrassi: Ray Ablack briefly dated Melinda Shankar, who plays his younger sister.
 * Mrs. Browns Boys... Let's just copy/paste from wikipedia on this one. "Many of the main cast are played by O'Carroll's real-life family. Cathy Brown is played by his wife, Jennifer Gibney; Winnie McGoogan by his sister; Maria Nicholson by his daughter and her real-life husband plays her brother-in-law Trevor; Buster Brady by O'Carroll's son and Betty Brown by his daughter-in-law. The character of Dermot, is played by an actor who is a very close family friend of O'Caroll's."

Theater

 * Rebecca Caine played Cosette in the original, 1985 London production of Les Miserables, opposite Colm Wilkinson as Jean Valjean, Cosette's father-substitute. This got rather squicky rather fast when she was cast, several years later, as Christine in the original Canadian company of The Phantom of the Opera - opposite Colm Wilkinson as the Phantom.
 * George Hearn (The Broadway replacement for Len Cariou as Sweeney Todd) and Betsey Joslyn (replacement for Johanna, Sweeney's daughter) were married in real life before the production. This can be seen on the tour DVD.

Web Original

 * Me and My Dick can turn very gross very fast if you can not stop thinking about the last musical you saw the Official Couple in, A Very Potter Musical, where they played siblings Ron and Ginny Weasley.

Western Animation

 * In the Young Justice epsiode "Terrors", Superboy and Miss Martian, who have UST, pose as the Terror twins to go undercover and foil a breakout from Bel Reve prison.