Actress Kristen Stewart supposedly had a fling with director Rupert Sanders, according to a report.

Stewart attended the Teen Choice Awards with her Twilight co-star and real-life boyfriend Robert Pattinson just a few days ago, however an American magazine cover alleges she strayed away from the relationship.

Us Weekly magazine has plastered a photograph of her and Snow White and the Huntsman director Sanders on its cover that would indicate the two had a romantic relationship - what The Examiner described as "a series of hot sessions".

Meanwhile, a source told People magazine: "Kristen is absolutely devastated. It was a mistake and a complete lapse in judgment."

Reps for neither Stewart, Pattinson nor Sanders have commented on or moved to clarify what went down, including the possibility of whether this is all one big misunderstanding.

A source close to Pattinson told E! News that he has always found fame "very difficult and isolating" and has long thought of Stewart as "the only person who he can talk to about that”.

The source added: "He feels like they are both on the same level and they understand one another.

"He worships her. He doesn't think there is another woman on the planet… as beautiful and kind as her. He wants to be with her 24/7, he wants to marry her.

“As far as he is concerned, Kristen is his perfect match...Kristen is perfect to him. That's why he's always known that someday she would be his wife."

Sanders is married to 33-year-old model, Liberty Ross – who also starred in Snow White as Queen Eleanor. They have two young children, Skyla and Tennyson, together.

The article has since been removed from Us Weekly's website.