"Deeply sorry" ... Kristen Stewart with Robert Pattinson.

"Deeply sorry" ... Kristen Stewart with Robert Pattinson. Photo: Getty Images

What a difference a week or so makes.

Just as the frothing tweets quietened down about Robert Pattinson and Kristen Stewart falling for one another "before they even met", the actor has packed his bags and moved out of the LA home he shared with his actress girlfriend.

The move comes days after The Snowhite and the Huntsmen star's fling with the movie's married director, Rupert Sanders, 41, was blown open when camera footage showing the couple kissing went public.

Liberty Ross and Rupert Sanders attend the premiere of "Snow White and The Huntsman" in London.

Liberty Ross and Rupert Sanders attend the premiere of "Snow White and The Huntsman" in London. Photo: Getty

Stewart, 22, called the slip a "momentary indiscretion" - but the ramifications are clear. Not only has Pattinson left their home but Sanders' wife, model and actress Liberty Ross, and two children are sure to have been left reeling.

To add insult to injury, the raven-haired, alabaster-skinned Ross, 33, played the role of Stewart's mother in the Snowhite remake.

People magazine reports that Pattinson, 26, is "in seclusion" and is not in contact with his Twilight co-star, with whom he has been in a relationship for three years.

Kristen Stewart poses with director Rupert Sanders, with whom she has admitted having a fling.

Kristen Stewart poses with director Rupert Sanders, with whom she has admitted having a fling. Photo: Reuters

The infidelity has left Pattinson "angry" and "heartbroken" according to the magazine, a source declaring: "I’m not sure they’ll be able to recover from this.”

Stewart is clearly keen to try, though.

"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 an apology to People magazine on Wednesday.

"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."

In a twist of premonitory fate, Pattinson had recently told Vanity Fair magazine that he did not understand infidelity.

"There's a thing I’ve never got. That is - why do people cheat?" he said to the glossy's April edition.

"I'm not the casual affair kind of guy. If I choose to be with someone, it's because I really want it. When I have a relationship, I'm 100 per cent with it."

But it's not just Stewart's boyfriend and Sanders' family who are affected by the news. Hundreds of Twilight fans have spoken up about being devastated by the split and Stewart's cheating.

One devoted "Twi-hard" has published a film of herself crying, apparently distraught at the news, though many seem to be in a state of denial, unwilling to accept Stewart's public admission of the facts.

Sanders issued an apology of his own, telling Reuters that he is "utterly distraught about the pain I have caused my family.

"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."

Radar Online reports that the actress is confident she can smooth things over. "Kristen is pulling out all the stops with Rob, completely apologising and trying to make things right with him, but she is very confident that she is going to win his trust back," a source told the site.

"Kristen is doing everything in her power to keep Rob from breaking up with her. She knows how much he loves her and she really believes that she is going to keep him from dumping her."

The couple are due to promote their next installment in the vampire saga together, a commitment that may prove awkward at best.