Watch Billy Joel & Jimmy Fallon Record Song Using iPad App

Billy Joel and Jimmy Fallon performed in four-part harmony last night.  Well, kind of, anyway.

On last night's "Tonight Show" broadcast, Jimmy Fallon demonstrated a voice-looping iPad app to singer Billy Joel, which the two then used to perform a mostly a cappella version of "The Lion Sleeps Tonight" with a four-part backing track of themselves.

Here's the video of Billy Joel joining Jimmy Fallon....