Will Smith Spontaneously Performs Summertime on Letterman [VIDEO]

Fun performance of the Fresh Prince's "Summertime" going viral!

Here's a fun clip from earlier in the week from The Late Show With David Letterman!  Will Smith was coming in to be a sit-down guest.  He seemed a bit surprised when the band played him in to his classic Fresh Prince jam with DJ Jazzy Jeff "Summertime."  He was so excited to hear the band play his song, he actually stole a mic and dropped some lyrics right there on the spot!  Check out the Fresh Prince in all of his glory right here!