On-screen siblings who were a real-life couple

Film sets are a known breeding ground for romance, with countless celebrity flings budding amidst emotional scenes and dramatic artificial rainfall. But what happens when you're interested in someone you're supposed to be siblings with? Apparently that might not be such a deterrent!

Check out this gallery to see which other on-screen siblings decided to push things forward when the cameras weren't watching.

Lisa Rinna and Patrick Muldoon, 'Days of Our Lives'

It certainly wasn't easy for Lisa Rinna and Patrick Muldoon when they were working together on 'Days of Our Lives' back in the '90s. Rinna played Billie Reed on the soap opera, while Muldoon played her on-screen brother, Austin Reed. Decades later, while being interviewed about her time on the show, Rinna revealed that she had an affair with Muldoon! Although she later corrected herself: "Well, not an affair, but a couple of one-night stands." If you're into watching re-runs of '90s soap operas, you'll never see this one the same way again. 

Blake Lively and Penn Badgley, 'Gossip Girl'

But that only meant that after the two had broken up in real life, they had to keep playing lovers for the duration of the show.

Matthew Broderick and Jennifer Grey, 'Ferris Bueller’s Day Off'

In 1987, the pair was in a car crash that killed two people, caused by Broderick who was driving on the wrong side of the road. The traumatic experience altered Grey's career and ultimately ended their relationship.

Will Arnett and Amy Poehler, 'Blades of Glory'

They did such a good job at making viewers laugh and cringe, but unfortunately the pair divorced a few years later.

Maureen McCormick and Barry Williams, 'The Brady Bunch'

McCormick recounted her exact thoughts when first making out with Williams in her 2008 memoir: "Oh my God! I’m kissing my brother. What am I doing?"

Emily VanCamp and Chris Pratt, 'Everwood'

Before Pratt was an A-lister, he dated his on-screen sister for three years. “We’ve pretty much gotten used to the response of, ‘Ew, that’s weird. That’s creepy,’” he told TV Guide.

Robert Pattinson and Nikki Reed, 'Twilight'

Before Kristen Stewart, there was Nikki Reed, also known as Edward Cullen's adoptive sister. Imagine navigating that love triangle later on set—yikes.

David Cassidy and Susan Dey, 'The Partridge Family'

Dey had a huge crush on Cassidy, who reportedly paraded his other dates in front of her until they finally ended up having a one-night stand that went nowhere.

Michael C. Hall and Jennifer Carpenter, 'Dexter'

They separated a few years later, around the same time the writers had arranged for their characters to have an incestuous story line, which the divorcees then had to play out.

Ian Somerhalder and Maggie Grace, 'Lost'

The tension between stepsiblings Boone and Shannon was an early plot point for 'Lost,' and was apparently fueled by a real, but short-lived, chemistry.

Lauren Graham and Peter Krause, 'Parenthood'

They had to keep playing siblings until the show's end in 2015, but they have stood the test of time. Graham even got Krause a role on the 2016 'Gilmore Girls' revival as the park ranger!

Katherine Heigl and Jason Behr, 'Roswell'

The two dated briefly in 1999 when they played siblings on the TV show 'Roswell.'

Kirstie Alley and Parker Stevenson, 'North and South: Book II'

The pair had been married for three years before they played brother and sister Billy and Virgilia Hazard in the 1986 miniseries.

Mark Hamill and Carrie Fisher, 'Star Wars'

Hamill revealed how it had transpired, involving a bit of liquid courage. He told her, "I think I’m a fairly good kisser," and then, "next thing you know we’re making out like teenagers!”

Jamie-Lynn Sigler and Robert Iler, 'The Sopranos'

Meadow and A.J. Soprano were seen being quite affectionate together off-screen, though they later denied they were involved.