By Will Robinson
Updated June 06, 2016 at 09:33 PM EDT
Credit: Harry Hamburg/NY Daily News Archive via Getty Images

Michael J. Fox, the actor and one of the most prominent public figures afflicted by Parkinson’s disease, honored the late Muhammad Ali, who died Friday evening, with a moving remembrance, calling him “sharp as a tack,” adding Ali was “magic.”

“It’s very tough to keep an even keel, but it’s something that you have to do to go forward and enjoy life. You can’t stomach other people’s projections of what you should be feeling. Muhammad was a perfect example of that,” Fox told Rolling Stone. “I mean, the whole world projected their fears for him onto him. And he took it all with love, with confidence and with humor.”

Beyond his athletic and humanitarian work, Ali was one of the highest-profile faces of Parkinson’s. He reached out to Fox after his diagnosis in 1991, but it took a while for the Back to the Future star to call back due to nerves.

“Finally, I called from the bathroom phone so I wouldn’t be interrupted. One foot was up on the toilet lid, and the phone was up to my ear,” Fox remembered. “Very quietly, he said, ‘I’m sorry you have this [disease], but with you in the fight, we have a better chance of winning.'”

Ali — who was diagnosed with Parkinson’s in 1984 — worked with Fox and his Foundation for Parkinson’s Research. They even produced a humorous PSA together, which ends with Ali knocking Fox out. One thing stood out to Fox during filming.

“I realized that no matter how famous you are, no matter how big a TV star you are – or whatever flimsy kinds of fame I had – you’re invisible when you’re with Muhammad Ali,” he said. “You’re anonymous. He attracts people like honey attracts bears. People come out of nowhere, to touch him and say hello to him. He was global.”

Read Fox’s full letter at Rolling Stone.