Justin Timberlake and Jimmy Fallon Return to Saturday Night Live on December 21st. [VIDEO]

Jimmy Fallon and Justin Timberlake have teamed up on "Late Night with Jimmy Fallon" 12 times over the past four years and they've done some hilarious bits, including their awesome "History of Rap" series.

And they're joining forces again next month on "Saturday Night Live".  Jimmy is hosting the December 21st episode, and Justin is the musical guest.

Meanwhile, NBC has announced that Paul Rudd will host the December 7th episode, with One Direction as the musical guest.  And John Goodman is hosting on December 14th, when Kings of Leon will perform.