Jimmy Fallon Sings A Cappella Duet With Billy Joel

Billy Joel, 64, who is still touring and plays a monthly gig at New York City's Madison Square Garden, stopped by the Tonight Show where he and Jimmy Fallon used the app'Loopy' to create a four-part backing track of themselves to sing 'A Lion Sleeps Tonight' a cappella. Let's just say, there's a certain former host who must be eating his heart out.