Michael J. Fox is getting candid about life with Parkinson's disease, and the moment he decided to step away from acting for good.

The "Back to the Future" star recalled that during filming for "The Good Fight," a spin-off of legal drama "The Good Wife," he couldn't remember his lines -- an incident that reminded him of a scene in Quentin Tarantino's "Once Upon a Time in Hollywood."

"I thought of 'Once Upon A Time In Hollywood.' There's a scene where Leonardo DiCaprio's character can't remember his lines anymore. He goes back to his dressing room and he's screaming at himself in the mirror. Just freaking insane," Fox said in an interview with Empire. "I had this moment where I was looking in the mirror and thought, 'I cannot remember it anymore.'"

The star added that he dealt with the realization calmly, saying to himself: "'Well, let's move on.' It was peaceful."

Fox, who rose to fame as Alex P. Keaton on the hit 1980s sitcom "Family Ties," was diagnosed in 1991 with the incurable degenerative disease, which affects the nervous system and motor skills including walking and speech.

The five-time Emmy Award-winning actor, who also has four Golden Globes, a Grammy and two Screen Actors Guild Awards, last month opened up to Jane Pauley for "CBS Sunday Morning" about how Parkinson's "is the gift that keeps on taking."

"I'm not gonna lie. It's getting harder," Fox said, adding, "Every day it's tougher."

His life with his family, and how living with Parkinson's affects their day-to-day reality, will be covered in the new documentary "Still: A Michael J. Fox Movie," which lands on Apple TV+ on Friday.

The actor explained in the CBS interview that he recently underwent spinal surgery for a benign tumor, and has suffered two broken arms, a broken hand and broken bones in his face as a result of falls.

"(Falling) is a big killer with Parkinson's," Fox noted. "It's falling, and aspirating food and pneumonia -- all these subtle ways that (it) gets you. You don't die from Parkinson's. You die with Parkinson's."

But the actor also mentioned that he's been living with the disease for "30 plus years," and that his "life is set up so that I can pack Parkinson's along with me if I have to."

"I recognize how hard this is for people, and I recognize how hard it is for me, but I have a certain set of skills that allow me to deal with this stuff," he told Pauley. "And I realize, with gratitude, optimism is sustainable."

"If you can find something to be grateful for, then you can find something to look forward to, and you carry on," he said.

Fox told Empire that he still has big plans following his retirement from acting -- for one, he will be putting his efforts into the Michael J. Fox Foundation for Parkinson's Research, founded in 2000, where, he said, "there's some really big stuff going on."