Was it just a snog or something more?
But last month, he invited her to Reese Witherspoon‘s California ranch to talk about a reunion.
During their meeting, Kristen insisted she hadn’t slept with the dad of two – who’s trying to salvage his marriage to model Liberty Ross – reiterating that it was a ‘momentary indiscretion’.
Although Rob, 26, wants to believe Kristen, his pals say ‘he’d be crazy to’.
‘The pics of her and Rupert were passionate beyond belief,’ says a source.
‘It’s hard to imagine she didn’t take things further than kissing.
‘Rob feels humiliated and wants proof Kristen didn’t sleep with Rupert – so although it sounds extreme, he’s asked her to take a lie-detector test.
‘Kristen isn’t happy about it.
‘She hasn’t decided yet, but she knows she’s got a lot to make up for.’
Read the full story about Robert Pattinson and Kristen Stewart in Now magazine dated 29 October 2012 – out now!
SEE PICTURES Robert Pattinson and Kristen Stewart – a love story in photos