"It is with great sadness that we report the unexpected passing of George Peterson, a champion on stage and off," officials from the Mr. Olympia competition announced on social media.

Peterson was in Orlando when he died -- preparing for the Olympia competition -- which kicks off Wednesday.

The cause of George's death is not yet clear, but his coach and close friend, Justin Miller -- who found Peterson deceased -- provided additional details on his death.

Miller says Peterson was in incredible spirits the night before he died ... and was pumped for the upcoming competition.

However, the next day, Miller says GP wasn't responding to texts or phone calls ... so he became worried, and went to George's hotel room.

Inside, tragically, Peterson was face down on the floor, cold. Still, Miller, desperate to help his friend, called 911 and was instructed to do CPR.

Unfortunately, Peterson -- who likely passed several hours earlier -- could not be saved.

George was a constant figure on the bodybuilding circuit ... competing at shows across the country, including the Olympia 4 times.

Peterson won the Classic Physique competition at the 2019 Arnold Classic.

Many people from the bodybuilding and fitness world -- from athletes to fans -- have expressed sadness at Peterson's unexpected passing.