Has Kristen Stewart cheated on Robert Pattinson?

Twilight star Kristen Stewart has not been faithful to beau Robert Pattinson, it has been claimed. The 22-year-old actress is said to have cheated on him with a married director twice her age, reported People magazine. According to sources, Stewart has been caught in the arms of Snow White and the Huntsman director, Rupert Sanders. The 41-year-old filmmaker, who is married to British Vogue model Liberty Ross, directed Stewart in his $170m feature debut, which was released just last month. The duo apparently had a brief fling. "Kristen is absolutely devastated. It was a mistake and a complete lapse in judgment," a source said. "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," she added.