Frank Varey -- a boxing prodigy who had won multiple national titles -- died on Thursday at just 16 years old ... and the news devastated Tyson Fury, who called the fighter a "future world champ."
Varey was out swimming with friends in the River Dee in the UK on Thursday when he went missing ... and law enforcement says after hours of searching, they found his body in the water.
It's believed the young pugilist accidentally drowned.
The tragedy absolutely rocked the boxing world .