(Cover) - EN Showbiz - Robert Pattinson is said to be in "shock" that his long term girlfriend and Twilight co-star Kristen Stewart cheated on him.

The 22-year-old starlet admitted this week that she had a brief affair with her Snow White and the Huntsman director Rupert Sanders.

And now insiders have told RadarOnline that the British actor is just devastated by the betrayal.

"Rob is in shock that Kristen cheated on him, he is absolutely devastated," a source told the site. "But right now he doesn't want to say anything in public until he figures out what he's going to do."

The couple was seen together just four days ago at the Teen Choice Awards where they seemed to be very happy together.

But just a few days earlier on July 17, pictures were taken of Kristen and Rupert kissing and fondling each other in a car.

"Rob is really hurt by Kristen," the source added. "Catching her cheating is not at all what he expected from her."

Kristen said in her statement that she was "so sorry" and that she loved Rob while Rupert's apology to his wife is in the hope that he can keep his family together. (C) Cover Media