In "Back to the Future 2," Marty McFly traveled to today, October 21, 2015. Now that we're actually living in the future, it's hard to imagine anyone other than Michael J. Fox playing that part -- but the role almost went to someone else.

Thirty years ago, Eric Stoltz was originally cast in the part of the 1985 classic "Back to the Future," until director Robert Zemeckis pulled the Golden Globe-nominated actor aside on set and gave him the bad news that things weren't working out.

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"It happened so fast," Fox told ET in 2010. "They told me about it, gave me the script, and two days later I was in a parking lot in Pomona with flames between my legs and Chris Lloyd running around like a crazy man."

Back in 1985, Fox revealed the secret to playing Marty during an ET interview.

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"What this role called for really was kind of a little peppy, excitable, vulnerable, strange guy who could kind of be cool but goof up," a young Fox said at the time.

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Fox took the role to ensure he would be remembered for more than just his "Family Ties" character Alex P. Keaton.

"Alex is very structured, whereas Marty is just a Rock 'n' Roll kid who's just trying to get by in life," Fox said. "It's been a lot of fun for me. It's a little closer to who I think I am."

In taking over the role, Fox had an uphill battle in terms of winning over his co-star Lea Thompson, who was fiercely loyal to her friend Stoltz, who was given the boot. She eventually was overcome by Fox's sheer talent.

"He was at the top of his game because he was doing 'Family Ties' at the same time," Thompson told ET recently. "So he could get a laugh wherever he needed it and that's a really amazing skill. Trust me, I do not possess it. He did a lot of falling and prat falls and squeaky voices and double takes and stuff that's good, old-fashioned comedy and he is good at it."

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Little remains of Stoltz's version of Marty McFly in the final product, but Thompson revealed that not everything got tossed out.

"There is a whole skateboard sequence where they had the same stunt man," Thompson said. "They didn't want to redo the stunts, so they made Michael Fox put his hair back and make it redder to make it match."

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