According to the article inside U.S. Weekly:
Robert Pattinson’s biggest fear has been realized.
On July 17, the 26-year-old actor’s girlfriend and Twilight costar, Kristen Stewart, 22, was caught in a series of steamy rendezvous with her Snow White and the Huntsman director, Rupert Sanders, 41 — and only Us Weekly has the photographic evidence.
Sanders — married to British Vogue model Liberty Ross, 33 — has two children, ages 7 and 5. During his marathon makeout session with Stewart, “it seemed like they couldn’t get enough,” according to one photographer.
Reps for both Stewart and Sanders had no comment.