Christopher Lloyd admits he was 'worried' about Michael J. Fox replacing Eric Stoltz in 'Back to the Future': 'But it all worked out'

• Lloyd said producer Steven Spielberg told the whole cast and crew of the recasting.
• "I had no idea a change was coming," Lloyd told GQ, admitting he was "worried" about the decision.

It's one of the greatest recastings in Hollywood history.

Though Michael J. Fox will be forever known for playing Marty McFly in the hit 1985 movie "Back to the Future" and its sequels, he was not originally cast to play the lead.

Eric Stoltz had the role. But when he was suddenly replaced in the middle of shooting, Lloyd — who played zany inventor Dr. Emmett Brown, whose friendship with a high schooler leads to a time travel adventure — was initially "worried."

In an interview with GQ looking back on his career, the 83-year-old actor said, "I had no idea a change was coming."

"One night we were shooting the mall beginning sequence," Lloyd continued, "we were asked to come to one of the trailers at one o'clock in the morning, and [Steven] Spielberg was there and he made the announcement of the change."

For the first six weeks of production on the time travel movie, young heartthrob Stoltz played McFly. Rising up the ranks in stardom thanks to roles in 1982's "Fast Times at Ridgemont High" and the soon-to-be-released 1985 drama "Mask," Stoltz was thought to be perfect in the role.

However, Stoltz was gone after a matter of weeks, and Fox, best known at the time for playing Alex P. Keaton on the popular 1980s TV show "Family Ties" and the original first choice to play McFly, had the role.

Lloyd said the reason for the recasting was that the producers needed more comedy out of the role. "They just decided they needed somebody with a comic flair," he added.

Still, Lloyd's big concern was wondering if he could capture the same energy embodying Doc Brown when shooting the scenes over again with a new actor.

"I was really working to get Doc right," he said. "I thought, 'I don't know if I can get it up to do that again.' So I was worried about it. But, it all worked out."

The result was Fox and Lloyd's characters becoming one of the famous duos in movie history.

"We had a chemistry, which lasted the whole time," Lloyd said of working with Fox. "We could come back after a break and it would just be there. You didn't have to work for it, which was great."