The French star, 38, recently performed a show at Koko in Camden, London, and after Ross, 50, had waited for over an hour to see her and get a picture, she reportedly refused.
An eyewitness said to UK newspaper Evening Standard: 'No one could quite believe it. Jonathan is one of the most high-profile faces on British TV and she was just so incredibly rude to him.
'She was being fawned over by swathes of lackeys and well-wishers, and couldn't even give him a minute.'
Ross reportedly laughed off the incident and left the show soon after.