Cameron Diaz and Robert Pattinson on October 27, 2012 in Los Angeles, California. Credit: John Sciulli/Getty Images

Seems Cameron Diaz isn't caught up on celebrity news.

The single actress, 40, ferociously flirted with Robert Pattinson -- who reconciled in early September with Kristen Stewart -- at the Gucci-sponsored L.A. County Museum of Art's Art + Film Gala on Oct. 27.

"She was pretty obvious," says one of three witnesses who watched Diaz come on to the Twilight star, 26. "Cam was seated next to Rob at dinner. She was touching his arm, doing her big Cameron laugh at everything he said and trying really hard. He was polite, but not having it."

Clearly he only has eyes for Stewart.

Just two days earlier, at a Prince concert at Hollywood Sayer's Club, Pattinson and Stewart couldn't keep their hands (or lips!) off each other.

"They were inseparable -- kissing passionately," says a concertgoer. "It was like watching one of their movies!"

The Brit even persuaded his standoffish sweetheart, 22, to dance with him.

Says the onlooker, "Rob was grinning the entire time."