Michael J. Fox Reflects on an Act of Kindness from River Phoenix 31 Years Later: 'He Was So Nice to Me'

There is one memory that has stuck with Michael J. Fox after all these years.

As part of PEOPLE's latest cover story, the retired actor opened up about his unexpected brush with Southern hospitality courtesy of the late River Phoenix. The moment in question occurred 31 years ago as Fox, 61, filmed 1991's Doc Hollywood in a small Florida town.

"River Phoenix and his brother [Joaquin Phoenix] had a place there, and River would take us out," Fox recalls. "He used to come and scoop us up and take us to his place and have a barbecue. It's funny because that was an act of kindness that was built on an act of kindness."

RELATED: Joaquin Phoenix Thanks Late Brother River for Inspiring His Acting Career in Emotional Speech

Fox believes the thoughtful gesture stemmed from his own act of kindness toward River, which occurred on the set of Fox's former series Family Ties. River — who died at 23 in 1993 from combined drug intoxication — served as a guest star in a previous episode.

Related video: Michael J. Fox jokes about the benefits of being an empty nester

"He did an episode of Family Ties when he was younger. It was just before or just after Stand by Me and he would do a scene and I could tell," Fox says. "I was looking at this guy ... I think Tracy [Pollan, my wife] was on the show that episode. And I said, 'Look at this kid working. This kid is taking this 10 ways from Sunday and he is really coming at it' ... I mean, kids don't act like this. He really knew how to be an actor but he was struggling on this one scene."

A teenage River received a pep talk from Fox after having a hard time with a particular scene.

"So I went up to him and I said, 'What's the problem?' And he said, 'I feel like a d—,'" Fox recalls. "And I said, 'You feel like a d—? Why?' He said, 'I feel goofy, I feel like a d—.' And I said, 'Welcome to the business. That's it. That's the highest level of accomplishment you'll get is to feel like a d—.' It's stupid. It's a stupid thing to do for a living."

Fox continued, "We pretend we're other people for a living. We use things that we're not really using and we eat things that we're not really eating and we stand in a place because the light's better there and it's all goofy, but if you stick with it, you can find a way to tell a story that other people can't."

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And ultimately, Fox says the late actor was "phenomenal" at the time.

"I guess that's why he was always so nice to me when he became a huge star," he adds.

For more from Michael J. Fox, pick up the latest issue of PEOPLE, on newsstands Friday, or subscribe here.

Acts of kindness are important to Fox, who has lived with Parkinson's disease for several decades and launched The Michael J. Fox Foundation in 2000. The foundation has since raised over $1.5 billion for Parkinson's research and therapies.

"Everything we did, the motive was pure. We know the agenda. I just want to cure Parkinson's," he tells PEOPLE. "We just want to get it done."