The relationship between Kristen Stewart and Robert Pattinson has been rocked by claims that the actress had a brief fling with a married director.
Stewart's hookup with Snow White and the Huntsman director Rupert Sanders - who is married and has two children - is believed to have occurred recently.
"Kristen is absolutely devastated," People magazine quoted one source as saying.
"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," the source said.
Meanwhile, Us magazine revealed on Tuesday that it's set to publish photographs of a "marathon makeout session" between Stewart and Sanders.
It said that the 41-year-old and his dark-haired woman were caught in a series of clinches on July 17 and "it seemed like they couldn't get enough."
Kristen Stewart and Rupert Sanders
The 22-year-old actress and Pattinson, 26, were all laughs just days ago at Comic-Con, even joking about their on-camera smooching scenes.
The couple met on the first Twilight set and reports began almost immediately that they were a couple.