Too much glitter? Kristen Stewart caught cheating

Jul 24, 2012 at 9:37 p.m. ET

Kristen Stewart reportedly cheated on longtime boyfriend Robert Pattinson with a married father of two. What the heck was she thinking?

kristen stewart

Vampires may be eternal, but their love is not. Twilight heroine Kristen Stewart was reportedly caught cheating on her co-star and longtime boyfriend Robert Pattinson -- with Snow White and the Huntsman director Rupert Sanders!

Sanders (to the right of Stewart in the above photo), who just happens to be married to British model Liberty Ross with whom he has two kids ages 7 and 5, was busted having a marathon make out session with the female half of one of Hollywood's steamiest couples by roving photographers on July 17.

"It seemed like they couldn't get enough," one pap told Us Weekly.

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A source close to the actress told People she totes didn't mean it and wants to stick with Pattinson.

"Kristen is absolutely devastated," the insider explained. "It was a mistake and a complete lapse in judgment."

"She wasn't having an affair with Rupert. It was just a fleeting moment that shouldn't have happened. She never meant to hurt anyone. She's a good person who just made a bad choice."

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Stewart, 22, was last spotted with 26-year-old Pattinson just a few days ago at Comic-Con in San Diego where they were joking about their Twilight love scenes while promoting Breaking Dawn Part 2, the last segment in The Twilight Saga. They began their romance on the set of the first Twilight film and rarely address their relationship.

Reps for Sanders couldn't be contacted, while Stewart and Pattinson's reps had no comment.

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