Floyd Mayweather Rocks Out at Wanya Morris' Wedding, Sings Boyz II Men

Huge weekend for Boyz II Men singer Wanya Morris ... who married his girlfriend Amber Reyes in Aruba -- and Floyd Mayweather was right there to party his ass of with the happy couple!

The wedding was amazing -- the two tied the knot on the beach at the Ritz Carlton in front of friends and family. Amber looked beautiful. Wanya looked beautiful. It was great!!!

But, the reception ... THAT WAS OFF THE HOOK -- and featured Wanya and Amber slow dancing to the Boyz II Men classic, "I'll Make Love To You."

Halfway during the song, things went from romantic to ridiculous ... when the guests swarmed the dance floor and began serenading the couple along with the track.

Wanya's bandmate Shawn Stockman got in on the action -- same with Floyd -- as the whole party belted out the 1994 hit.