Wait until the end - the song they come up with is seriously impressive.
This throwback follows on from a series of nostalgic episodes from Mr. Fallon, including an amazing 'Saved By The Bell' reunion and a perfect re-imagining of Smith's classic 'Fresh Prince' opening.
The Tonight Show is recording in Los Angeles this week instead of New York, so they decided to recreate the legendary opening sequence and reunite the gang from Bayside High.
Last week he also got Will Ferrell singing along to Beyoncé's "Drunk In Love" and "Let It Go" from 'Frozen', while Kevin Hart lip-synced with tracks from John Legend and Katy Perry, and Fallon picked Kelly Clarkson and Dirty Dancing as his inspiration for an epic lip sync battle.
Basically, everything Jimmy Fallon does is brilliant and we don't even know why anyone else tries.