VIDEO: Eric Stoltz as the original Marty McFly

Everyone knows the classic 1985 film "Back to the Future" featured a boyish Michael J. Fox in a winning performance as Marty McFly.

But Fox was not the original McFly. In fact, Eric Stoltz was five weeks into shooting the famed McFly role when director and co-writer Robert Zemeckis made a drastic production decision -- changing his lead actor.

Details of the shocking Hollywood switch and never-before-seen footage of Stoltz as McFly are part of the extras package for the "Back to the Future 25th Anniversary Trilogy" to be released on Blu-Ray on Oct. 26.

Zemeckis says the casting change was "this horrific decision; it was heartbreaking for everybody."

Executive producer Steven Spielberg said that Zemeckis consulted him before pursuing the casting change.

"(Zemeckis) showed me the first five weeks of shooting that he had put together," Spielberg said. " And he said, 'I just don't think we're getting the laughs I was hoping we would get.' "

Spielberg said he realized his director "was absolutely correct."

The rest is pop-culture history. Zemeckis was able to "convince the studio to let me reshoot five weeks of work," and Michael J. Fox was cast in a career-defining role. "Back to the Future," released on July 3, 1985, would go on to gross $381 million worldwide and lead to two further sequels.