(Cover) - EN Showbiz - Kristen Stewart says she is "deeply sorry" for having an affair with married director Rupert Sanders.

It has been revealed that the 22-year-old actress cheated on her Twilight co-star and long term boyfriend Robert Pattinson with the man who was at the helm of her recent movie, Snow White and the Huntsman.

Kristen made the public apology today in a statement to People magazine.

"I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected," she said.

"This momentary indiscretion has jeopardized the most important thing in my life, the person I love and respect the most, Rob.

"I love him, I love him, I'm so sorry."

Kristen was pictured kissing the 41-year-old director and indulging in public displays of affection. Rupert is married to British Vogue model Liberty Ross and they have two children together.

Kristen and Rupert were seen cosying up together in her car on July 17 by a photographer.

"Kristen was sitting with her back up against the driver's side window and this guy was kissing her entire body," the snapper said but added that they were very wary about being caught.

Meanwhile, Rob recently said ominously that he "never understood why people cheat." (C) Cover Media