On 'Jimmy Kimmel Live' (weeknights, 12AM ET on ABC), Christian Slater recounted once meeting -- and singing with -- one of his heroes. At first he wouldn't say who it was. And his story about the encounter went on and on...

At a restaurant, Slater sent a bottle of wine to the mysterious celeb's table. Soon the two were chatting at the same table, and a woman came over and pestered his hero, saying, "I bet he doesn't even know how to play [piano] anymore."

OK, so we learned the guy's a musician. Before long, they both performed for the impromptu audience, with Slater belting out some Sinatra accompanied by "this dude" on the piano.

"Tell us who it is, Slater!" demanded Jimmy Kimmel. Slater answered, "It was Billy Joel. He was the sweetest, nicest guy and to get up there and do that, especially after this lady was ribbing him."

Watch the full interview here: