|Kristen Stewart and Rupert Sanders (Jordan Strauss / Invision)|
A source told website RadarOnline: "During the press junkets for 'Snow White and the Huntsman', Kristen was already close to Rupert's kids.
"She treated his eldest daughter to ice cream in Los Angeles when there was a break in her press interviews back in the latter end of May."
The insider continued: "At that time no one suspected anything was up - there was no reason to - but looking back at it now it seems pretty suspicious.
"The affair could have started back then - and everyone was blindsided. Why else would you take out a married man's kid for ice cream?"
Kristen issued a public apology to boyfriend Robert on Wednesday (25.07.12) where she called the illicit affair a "momentary indiscretion."
She said: "I'm deeply sorry for the hurt and embarrassment I've caused to those close to me and everyone this has affected. 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."
It came after Us Weekly magazine claimed the 'Twilight Saga' star and 41-year-old filmmaker could hardly keep their hands off one another and a series of photos confirmed the affair.
One photographer said: "He was all over her. [Kristen] would only take a break [from kissing] when they thought someone was walking by."