Things are about to get very ugly for Kristen Stewart and Robert Pattinson.

This week's UsWeekly cover story tells the tale of Stewart cheating on Pattinson with her "Snow White and the Huntsman" director, Rupert Sanders. The magazine says it obtained incriminating photos of the 22-year-old actress and Sanders, calling the moments caught on camera a "steamy rendezvous."

Sources tell People, "She wasn't having an affair with Rupert. It was just a fleeting moment that shouldn't have happened." The "rendezvous" allegedly occurred recently and, to add insult to cheating injury, Sanders, 41, is also...