Michael J. Fox and Christopher Lloyd had a few heavy conversations after reuniting following a roaring round of applause for the "Back to the Future" stars during a panel discussion at New York Comic Con.

The actors first worked together on the 1985 hit sci-fi flick directed by Robert Zemeckis, a time traveling tale which has since earned the title as one of the greatest films ever made with two sequels, a musical, theme park rides and more in its multi-million dollar franchise. 

Fox initially wasn't even supposed to be part of the movie, and joined the production only after Zemeckis had filmed with Eric Stoltz. The director wasn't sold on Stoltz and replaced him with Fox, who became known for his leading role as Marty McFly. 

MICHAEL J. FOX REUNITES WITH HIS ‘BACK TO THE FUTURE’ COSTAR CHRISTOPHER LLOYD ON INSTAGRAM: ‘BACK TO BACK’

'Back to the Future' panel with Christopher Lloyd and Michael J. Fox

Christopher Lloyd and Michael J. Fox reunite at New York Comic Con for "Back to the Future" panel. (Getty Images)

"The announcement — at one o’ clock in the morning after we were shooting for six weeks — was that the actor playing Marty would no longer be playing Marty, and that tomorrow, we would start shooting with Michael," Lloyd, 83,  said of the shocking change of actors, according to Syfy.com "I felt that I barely made it through the [first] six weeks, and now I was gonna have to do it again?!"

But the veteran "One Flew Over the Cuckoo's Nest" performer understood the switch.

MICHAEL J. FOX REFLECTS ON PARKINSON'S DIAGNOSIS: ‘GRATITUDE MAKES OPTIMISM SUSTAINABLE’

"The chemistry was there from the first scene we had, it was alive, and it remained that way for three movies," he said. "It hasn’t gone away, by the way."

Fox, 61, agreed that working with Lloyd came naturally.

Christopher Lloyd and Michael J. Fox

Christopher Lloyd recalled how he wasn't even supposed to work with Michael J. Fox on "Back to the Future." (Mike Coppola)

Christopher Lloyd and Michael J. Fox

Christopher Lloyd and Michael J. Fox hug onstage at the "Back to the Future" reunion.  (Bryan Bedder)

"All I had to do was just react," he said. "Just take it in and let it wash over me. I thought he was brilliant. That was the whole thing: be with Chris and let it be Chris, and enjoy it … It was a thrill. Anytime I got to work with him, I knew it was gonna be a good day."

"Back to the Future," which also starred Lea Thompson, Crispin Glover and Claudia Wells was made on a $19 million budget and has earned nearly $400 million at the box office

CLICK HERE TO SIGN UP FOR THE ENTERTAINMENT NEWSLETTER

The film received an Academy Award for best sound effects editing, and three additional nominations, including best original song for "The Power of Love" by Huey Lewis and The News. 

Zemeckis also followed up with two sequels in 1989 and 1990. 

Fox played Marty McFly

Claudia Wells and Michael J. Fox on the set of "Back to the Future." (Sunset Boulevard/Corbis)

Both Lloyd and Fox continued starring in films and television shows after the success of the movie, but Michael revealed he retired from the business in his 2020 memoir "No Time Like the Future" due to the progression of his Parkinson's disease diagnosis

"You guys have given me my whole life," Fox said. "The best thing that happened in my life was this thing. Parkinson's is a gift. I've said to people it's a gift and they say, 'You're nuts.' I say, 'Yeah, but it's the gift that keeps on taking.' But it's a gift and I wouldn't change it for anything ... It's not about what I have, it's about what I've been given."

Channeling his Doc Brown character, Lloyd gave the crowd a few parting words of wisdom. "It was said once in a movie, the future is what you make it."

CLICK HERE TO GET THE FOX NEWS APP