BRIT film star Robert Pattinson has been left devastated after girlfriend Kristen Stewart reportedly cheated on him with an English film director twice her age. According to US reports, Rob’s Twilight co-star Kristen, 22, was caught in a steamy clinch with her Snow White and the Huntsman director Rupert Sanders, 41, a week ago. Sanders is married to British Vogue model Liberty Ross, 33, and the couple have two children aged seven and five. Robert and Kristen have been Hollywood’s golden couple since starring together in teen hit Twilight. A witness said: "It seemed like they couldn’t get enough.” A source close to Kristen last night called the fling a "lapse of judgment”. The insider said: "Kristen is absolutely devastated. It was a mistake. "She never meant to hurt anyone. She’s a good person who just made a bad choice.” The Sun