Kristen Stewart may have called her affair with Rupert Sanders a "momentary indiscretion," but now the director's brother-in-law has come forward to claim what has already been suspected: the pair have been hooking up for months.

Leopold Ross, the brother of Sanders' actress wife, Liberty Ross, told the Brit newspaper, The People:

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

Since Snow White and the Huntsman shot from September 19 to December 10, 2011, Leopold says the affair actually started last fall, which explains why Stewart was on set most days of filming, even when she wasn't in the actual scenes.

Ross, who played the Twilight star's mother in the flick, left England with Rupert so that he could pursue his career as a director in Hollywood, but her brother says:

    “She made some sacrifices for something she thought was worth it, now she knows, right? Five minutes from her home.... Doubt it was worth it but it’s life. It might actually make things better in the long run. She wasn’t that happy for a while, but our family is close, she’ll be all right."

We recently spotted moving trucks outside of the lavish Los Feliz home Robert Pattinson and Stewart share, which they have both since moved out of, after the cheating scandal broke this week.

Aside from the looming press tour for the finial Twilight flick, Stewart and Pattinson are also slated to appear together at MTV's Music Video Awards September 9.

Will they work it out by then?