Well, that was epic.

The Late Show released a clip on Wednesday, Jan. 6 of host Jimmy Fallon, Whiplash star J.K. Simmons, and music sensation Billy Joel joining his band in an impromptu musical performance of the singer's famous hit “The Longest Time.”

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During this "commercial break" video, it's evident that the unforgettable moment was completely unplanned — yet it still might be one of the best late-night television show's happenings to date!

Tune in to the video below!