Rupert Sanders and Kristen Stewart Affair Lasted for Months, Relatives Claim

It was a one-time mistake. That's the line Kristen Stewart is hoping will keep Robert Pattinson from leaving her, although early indications don't bode very well for the future of Robsten.

But is that claim even valid? Did Stewart really just make out with Rupert Sanders for a few fleeting moments? Or was this affair far more drawn out and calculating?

Rupert Sanders likes what he sees at the premiere of Snow White and the Huntsman.

Relatives of the Snow White and the Huntsman director say it's the latter. They cite a photo of Sanders and Stewart in Berlin on May 15 as evidence, with Sanders' brother-in-law  telling People UK of the cheating:

"It was from the last half of filming and all through post-production, clear into last week.”

Whether it lasted for one minute or one month, what would prompt Kristen to do such a thing? Jealously, insiders allege.

Pattinson supposedly grew especially close to Remember Me costar Emilie de Ravin and, even if nothing romantic was ever rumored between the pair, Stewart reportedly took issue with the relationship.

“She found it difficult to cope with Robert being close friends with another woman," a source tells the publication. "As their friendship grew, she ­became more envious to the point that she would be very upset."

Going forward, Pattinson and Stewart will be faced with issues beyond the personal. On a professional front, they are scheduled to begin promotion for Breaking Dawn Part 2 in October.

But "Robert won’t see Kristen and is refusing to do any joint ­personal appearances with her," this source adds. "This is a potential nightmare for all involved."