Credit: Kevin Winter/Getty Images.

Kristen Stewart apologized today for cheating on her boyfriend of three years, her "Twilight" co-star Robert Pattinson, with her "Snow White and the Huntsman" director, Rupert Sanders.

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

Sanders, 41, is married to model Liberty Ross, 33. They have two children together. He also issued an apology to People.

"I am utterly distraught about the pain I have caused my family," he said. "My beautiful wife and heavenly children are all I have in this world. I love them with all my heart. I am praying that we can get through this together."

Us Weekly first reported Stewart and Sanders' affair. The magazine featured a photo of Sanders kissing Stewart on its latest cover.

Pattinson, 26, and Stewart, 22, fueled the frenzy over the "Twilight" movie series with their real-life romance. The two never publicly confirmed that they're a couple, but they've become increasingly open about their relationship, kissing in public and letting themselves be photographed while on dates.

A representative for Pattinson did not immediately respond to ABCNews.com's request for comment.

In 2010, Stewart told Elle magazine that she didn't want to "cheapen" her relationship with Pattinson by talking about it.

"I would never cheapen my relationships by talking about them," she said. "People say, 'Just say who you're dating. Then people will stop being so ravenous about it.' It's like, No they won't! They'll ask for specifics."