The CANDY SHOP star, real name CURTIS JACKSON, and former boyband member Williams both checked into the Ritz-Carlton hotel in Berlin, but trouble reportedly brewed when Williams' fans mistook 50 Cent's car for the former TAKE THAT singers' and greeted the rapper chanting, "Robbie, Robbie."
The situation escalated when Williams later complained to hotel management, demanding they curb the hip-hop wildman's late night antics.
But 50 Cent has another explanation for their falling out - Williams felt humiliated because the hip-hop star refused to meet him.
He says, "He's a sucker. He said I was keeping him awake.
"I know he wanted to meet me but I didn't have time. Maybe that's why he was upset."