We're just so glad he seems happy!
The source spilled:
Awww that's so amazing!
The insider added:
[Image via Guillermo Proano/WENN.]
Is it just us, or is Jimmy Fallon having the most fun anyone has ever had on TV?
And now he's dueting with music legend Billy Joel!
Ch-ch-check out the video (above) to see the duo duet to doo-wop!