Kristen Stewart [photos] allegedly cheated on Robert Pattinson with her married 'Snow White and the Huntsman' director, Rupert Sanders.
"Kristen is absolutely devastated," one source tells People magazine. "It was a mistake and a complete lapse in judgment. 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."
Meanwhile, Us Weekly has also obtained a photo (pictured right) that shows Stewart and Sanders may have shared more than a working relationship.
But Pattinson wasn't the only one blindsided. It also came as a shock to Sanders wife, 33-year-old model-actress Liberty Ross, who simply posted "Wow" on her Twitter page and closed her account, hours before the news went public.
She had also written an earlier message about the film's world premiere that included a picture of her with the 22-year-old Stewart, but that has since disappeared as well.
Ross starred in 'Snow White and the Huntsman' as Stewart's mother in the movie, Queen Eleanor.
Sanders, 41, and Ross have two young children together.
