Paula Abdul caught Keanu Reeves "doing air guitar in his underpants" as the two filmed her Rush Rush music video.

The 57-year-old singer addressed rumours the pair had dated during an appearance on Watch What Happens Live on Wednesday, when a caller asked her: "Paula, were the rumours true that you were dating Keanu Reeves after he starred in the Rush Rush video. Please say yes!"

"I wish," the Straight Up hitmaker jokingly responded, before revealing how she accidentally stumbled upon the star dancing around his dressing room wearing nothing but his pants on the set of the 1991 shoot.

"It was like the funniest thing. I wanted to introduce myself to him, I hadn't met him yet," she recalled. "And I went up to his trailer and the door was slightly open. He had headphones on and he was air guitaring in his underwear.

"I said, 'That's my boyfriend.'"

When host Andy Cohen pressed her again as to whether she and Keanu were romantically involved, she insisted: "No."