And here are the videos to prove it... Who knew Paul McCartney knew how to play 'Shake It Off'?! Then Miley Cyrus played a dirge about the death of her gold fish, before being joined by Ariana Grande. Then Debbie Harry got involved, so did Michael Bolton (true story), The B52s, Bill Murray (avec tambourine), Elvis Costello - and then Prince arrived. In a haze of "purple smoke." THIS HAPPENED. 

D'you know what the most impressive thing is, though? That JIMMY FALLON IS A MACHINE who can take charge of a "celebrity mosh pitt" AND then host his own live late night talk show a few hours later. What. A. Legend.