Will Smith -- 'Fresh Prince' Stars REUNITE to Support Will's Son

Now this is the story all about how Will Smith, DJ Jazzy Jeff and Alfonso Ribeiro reunited this week -- IN EUROPE -- and it was all to support Will's son.

"The Fresh Prince of Bel-Air" trio were chillin' out, maxin' and relaxin' at a London club Thursday night to see Will's older son Trey DJ.

Fun Fact -- the mini-reunion went down 17 years -- almost to the day -- after the show went off the air.