Mischa Barton and Claire Danes cheat

Two longtime Hollywood romances are on the rocks because of on-set hanky panky between co-stars. Both Mischa Barton and Claire Danes are said to have cheated on their boyfriends: Cisco Adler and Billy Crudup, respectively, while filming their latest movies.

According to the New York Daily News, Mischa had a fling with actor Fran Kranz while in North Carolina shooting Don't Fade Away. An insider said, "They hooked up on the set in North Carolina. But I wouldn't say they were dating. It's more casual than that, even though it's ongoing." Kranz is a high school friend of Jake Gyllenhaal, who is also rumored to have canoodled with Barton in the past.

Meanwhile, Claire, who allegedly broke up with Billy last month, is said to have mixed business with pleasure in Rhode Island while she filmed Evening. The lucky beneficiary of Claire's lust was her co-star, Hugh Dancy. A source on the set told NYDN that Danes and Dancy spent the night together on November 2, "with the door two feet ajar, and everybody listening." But Claire wasn't the only one who got a piece of Hugh during filming. The mole says, "The cast was pretty much drunk every night" and Hugh was also seen making out with the movie's screenwriter, Michael Cunningham and a male hotel manager. Looks like Claire doesn't mind if her men swing both ways.