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Looks like we have a little bit of insight as to what happens during the commercial breaks of "The Tonight Show Starring Jimmy Fallon" based off this just-released footage from the hit NBC show featuring Billy Joel and J.K. Simmons

On Wednesday (January 6), NBC unveiled footage during the show taping's commercial break earlier that day, which features a pretty awesome "spontaneous doo-wop performance of 'The Longest Time' with Billy's band" while filming local promos.

If that wasn't enough, the music legend also offered fans a performance of Rolling Stone classic, "Beast of Burden," during his appearance.

Check out Billy Joel and Jimmy Fallon's performances below!

Photo: YouTube/The Tonight Show Starring Jimmy Fallon