1 of 16 Randy Tepper/Showtime
Michael C. Hall and Jennifer Carpenter, Dexter
As if Dexter's incestuous story line wasn't uncomfortable enough, consider the fact that these on-screen siblings used to be married! Hall and Carpenter eloped on New Year's Eve 2008 but separated two years later. Though they may no longer be an item in real life, the exes recently shared one of the most cringe-worthy romances when Deb (Carpenter) developed feelings for her — thankfully adopted — brother Dexter (Hall).
2 of 16 Byron Cohen/NBC/NBCU Photo Bank/Getty Images
Lauren Graham and Peter Krause, Parenthood
The two eldest Braverman siblings have been dating in real life since reconnecting on the NBC drama in 2010. Graham and Krause first met in 1995 when they both guest-starred on Caroline in the City. "It was just a funny timing thing," Graham told More. "We were friendly. But our lives went in separate directions. I would see him now and again. It wasn't like I thought, 'Oh, someday.'"
3 of 16 Ron Tom/ABC via Getty Images
Emily VanCamp and Dave Annable, Brothers & Sisters
OK, this one isn't totally icky, but it's close enough. VanCamp and Annable dated from 2007-08, after her character Rebecca was introduced as the half-sister of Justin (Annable) and his siblings. But it turned out that they weren't biologically related at all, which gave Justin the green light to woo Rebecca, marry her and divorce her.
4 of 16 Warner Bros./Everett Collection
Emily VanCamp and Chris Pratt, Everwood
VanCamp just can't get enough of her co-stars! (She's now with Revenge's Josh Bowman). But before dating her on-screen (almost) half-sibling on Brothers & Sisters, she dated Parks and Recreationstar Chris Pratt in 2004 while the pair were playing siblings Amy and Bright Abbot on the WB series.
5 of 16 ABC Photo Archives/ABC via Getty Images
Maureen McCormick and Barry Williams, The Brady Bunch
Though they played stepsiblings Marcia and Greg Brady, McCormick and Williams "couldn't keep [their] hands off each other" during filming, according to McCormick's 2008 memoir, Here's the Story. McCormick was 16 when she began dating Williams, who's two years her senior. In her book, she goes into disturbing detail about her crush on her on-screen stepbrother. "I was ready to lose my virginity to Barry, and it might have happened one night at his house if not for his parents busting in on us," she writes. Marcia, Marcia, Marcia!
6 of 16 Everett Collection
Shannon Doherty and Jason Priestly, Beverly Hills, 90210
When you're on a brand new show that becomes an overnight sensation and is filled with good-looking people, you're bound to hook up with each other. Just as his character Brandon kissed every girl he wasn't related to on the small screen, Priestly admitted to Howard Stern he also fooled around with his on-screen twin sister.
7 of 16 Adam Taylor/NBCU Photo Bank/Getty Images
Milo Ventimiglia and Hayden Panettiere, Heroes
Ventimiglia played Peter Petrelli, the uncle of Panettiere’s character Claire Bennett on the hit NBC superhero drama. They began dating about a year into the show, drawing some ire because of their age difference. (Ventimiglia is 12 years Panettiere's senior.)
8 of 16 Mario Perez/ABC via Getty Images
Ian Somerhalder and Maggie Grace, Lost
It might have been cute when Clueless’ Cher Horowitz fell for her stepbrother Josh, but there was something downright wrong with Boone's (Somerhalder) romantic obsession with his stepsister Shannon (Grace). Maybe that's why Somerhalder and Grace kept their real-life relationship a secret. The couple quietly dated in 2006, after both had been killed off the hit drama.
9 of 16 Mario Perez/ABC via Getty Images
Michael Emerson and Carrie Preston, Lost
Carrie Preston and Michael Emerson had been married for several years before they played mother and son on ABC's Lost. But they never shared the screen: Preston played Emily Linus, who died after giving birth to her son Ben, played as an adult by Emerson.
10 of 16 Robert Zucker/Warner Bros/Getty Images
Joley Richardson and John Hensley, Nip/Tuck
Nip/Tuck was always disturbing, but the most bizarre aspect of the series possibly happened when the cameras weren't rolling. For more than a year, Richardson was rumored to be dating Hensely, who played her teenage son. Thankfully, Hensely wasn't actually a teenager. In reality, the age gap between the couple was only 12 years. But that doesn't make it any less weird to treat your girlfriend like your mother and get paid for it.
11 of 16 Touchstone Pictures And Television/Getty Images
Evan Rachel Wood and Shane West, Once and Again
Evan Rachel Wood and Shane West didn't become an off-screen item until years after they played brother and sister Jessie and Eli Sammler on the short-lived ABC show. But while the pair remained coy about their relationship, they were photographed kissing and holding hands at several events in the summer of 2009. (They broke up in early 2010, when Wood reunited with Marilyn Manson.) Apparently Wood has a thing for her co-stars; in 2012, she married British actor Jamie Bell, whom she met in 2005 on the set of a Green Day music video.
12 of 16 BBC
David Tennant and Georgia Moffett, Doctor Who
Moffett and Tennant married in 2011, three years after Moffett played the cloned daughter Tennant's Doctor on the long-running BBC hit. Bonus oddity: Moffett's real-life father Peter Davison also played The Doctor in the 1980s. Sounds as confusing as some of The Doctor's time-travelling adventures!
13 of 16 ABC Photo Archives/ABC via Getty Images
Susan Dey and David Cassidy, The Partridge Family
The duo, who played siblings Laurie and Keith Partridge, reportedly had a fling during their time on the show. But the pair aren't friendly now, especially after Cassidy said in his 1994 autobiography C’Mon Get Happy that "Susan lacked the slutty aspect of a female that I always found so attractive.'' Dey didn't attend a 2010 Today show reunion of the cast, during which Cassidy said he wished to reconcile with her.
14 of 16 20th Century Fox Film Corp./Everett Collection
Katherine Heigl and Jason Behr, Roswell
It was love at first sight for Max (Behr) when he saw Liz (Shiri Appleby) on the alien drama, but Behr only had eyes for Heigl, who played his on-screen sis Isabel, in real life. The two started dating in 1999 and broke up in 2001, a year before Roswell ended. Fun fact: Behr is now married to KaDee Strickland, who starred on Private Practice, which was a spin-off of Heigl's old stomping grounds Grey's Anatomy.
15 of 16 HBO/Everett Collection
Jamie-Lynn Sigler and Robert Iler, The Sopranos
Sigler and Iler, who played siblings Meadow and A.J. Soprano on the HBO hit, were spotted "getting close" in a Vegas nightclub during The Sopranos' final season in 2007. However, Sigler and Iler — who basically grew up on the show — always denied reports of any off-screen romance, describing themselves in a 2007 interview with the Today show as "best friends" who would never be anything more.
16 of 16 Bruce Birmelin/Disney Channel via Getty Images
Selena Gomez and David Henrie, Wizards of Waverly Place
While the two have never copped to being more than friends, their recent pictures suggest otherwise. Could these two, who starred as siblings Alex and Justin Russo on the Disney Channel hit for six years, be hiding a secret romance?