Kristen Stewart Cheated On Robert Pattinson With Married ‘Snow White’ Director? Are The ‘Twilight’ Actors Over?

While Stewart and Pattinson never officially announced their relationship to the public, the co-stars have been seeing each other since the filming of Twilight in 2008. Unfortunately for Pattinson, their relationship has taken a bite out of a poisoned apple.

Us Weekly is reporting that Stewart, 22, had a marathon makeout session with Sanders on July 17. A photographer witnessing the scandalous situation reported that the director and actress seemed like they couldn't get enough.

A source told People that that Stewart's affair with the married director was only a brief fling, but that's enough to do the damage.

It was a mistake and a complete lapse in judgment, a source says of Stewart, who is reportedly devastated. She never meant to hurt anyone. She's a good person that just made a bad choice.

Stewart and Pattinson we're just spotted together on Sunday at the 2012 Teen Choice Awards. The pair seemed to be all smiles, unaware that scandalous pictures would put a strain on their relationship  a couple days later. If Pattinson was previously unaware of his girlfriends infidelities, he is bound to know now.

Sanders, who is married to 33-year-old British Vogue Model Liberty Ross, has two young children. Both reps for Sanders and Stewart has no comment, reports Us Weekly.

Us Weekly promises to have more incriminating photos of Sanders and Stewart's steams affair, along with their initial interaction, and the problem Stewart's fling will cause for Breaking Dawn Part 2 promotion. The magazine will be out on Friday, but to see a picture of Kristen Stewart and Rupert Sanders in an intimate embrace click here.