Will Smith -- Raps 'Fresh Prince' & Carlton Banks Returns!

Will Smith brought back the "Fresh Prince" theme song the last time he was on "The Graham Norton Show" -- so he decided to take it to a whole other level last night ... and brought back DJ Jazzy Jeff and Alfonso Ribeiro for an epic reunion.

With his son Jaden serving as hype man, Will once again resurrected the classic track, this time with Jazzy Jeff on the turntables. And when Alfonso came out to lead a Carlton Dance Party ... the whole place went crazy.

As for the final dance number ... Graham tried his best to keep up with the fellas, fellow guest Heather Graham rocked out from afar ... and Bradley Cooper just stood there and watched.