Michael J. Fox mulled retirement after 'Once Upon a Time in Hollywood'

Michael J. Fox revealed Leonardo DiCaprio's Once Upon A Time In Hollywood key scene was the cause behind his retirement.

Speaking to Empire, the Back To The Future recalled The Good Fight filming, where he forgot his lines because of Parkinson's disease.

"I thought of Once Upon A Time in Hollywood," adding, "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," he said.

Fox added: "I had this moment where I was looking in the mirror and thought, 'I cannot remember it anymore. Well, let's move on.' It was peaceful."

Previously, Fox also revealed a milestone in the research of Parkinson's disease cure.

Speaking to Lorraine Kelly on Friday's Lorraine, he added, "I feel it's [a cure] closer than it's ever been."

The veteran actor continued, "I think we've found this biomarker which is huge, identifying the disease and therefore being able to treat it earlier."

"It was a gigantic breakthrough, we didn't expect to make it this soon. We were working on it for a long time, ten years ago we talked about it."