In a Twitter post Thursday, the madman of metal said he is physically unable to withstand the impact of tour-related travel and has cancelled all upcoming concerts.

“This is probably one of the hardest things I’ve ever had to share with my loyal fans,” he wrote. “As you may all know, four years ago, this month, I had a major accident, where I damaged my spine. My one and only purpose during this time has been to get back on stage. My singing voice is fine. However, after three operations, stem cell treatments, endless physical therapy sessions, and most recently groundbreaking Cybernics (HAL) Treatment, my body is still physically weak.”

Osbourne has been delaying his world tour since he took a fall in 2019 and said he was “humbled” fans were still holding on to their tickets. Though he had hoped to retake the stage, he says he has come to the realization that he is “not physically capable” of doing the shows.

“Never would I have imagined that my touring days would have ended this way,” he wrote. “My team is currently coming up with ideas for where I will be able to perform without having to travel from city to city and country to country.”

Osbourne has been touring since the 1960s—and in his note, he thanked fans, family, his band and fellow Rock and Roll Hall of Famers Judas Priest (his tour mates) for their “endless dedication, loyalty, and support, and for giving me the life that I never ever dreamed I would have.”

Despite his injuries, Osbourne has managed to perform occasionally, including last September, when he performed during halftime at a Los Angeles Rams game. And he made it clear that while sustained touring is no longer possible, he does hope to continue to make occasional appearances.

“Believe me when I say that the thought of disappointing my fans really F***S ME UP, more than you will ever know,” he said.