By Christopher Rosen
Updated January 07, 2016 at 12:43 PM EST
Credit: Douglas Gorenstein/NBC

The best part of Wednesday’s The Tonight Show Starring Jimmy Fallon didn’t even occur on the show. While shooting promos for the broadcast, guest Billy Joel started an unrehearsed doo-wop performance of his hit song “For the Longest Time” with help from host Jimmy Fallon, fellow guest J.K. Simmons, and Joel’s band.

It was Simmons who suggested the song as the group milled about waiting to record the show’s teasers. After that it was off to the races, with the trio of stars harmonizing like pros.

“Come on! That’s the way to do it,” Fallon yelled after the performance was over. The group then filmed the promos, but were still on a high from what just transpired. “That was so fun,” Fallon said after the work was officially done.

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During the actual Tonight Show, Joel and Fallon sat down for an interview and also sang a cover of the Rolling Stones hit “Beast of Burden,” with Fallon affecting the vocal style of Mick Jagger for the performance.

And then after all that, Joel gave a proper performance of “Scenes from an Italian Restaurant” for the Tonight Show crowd. Good night for Billy Joel fans. Watch the showstopper below.

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