When audiences see 20th Century Fox’s “Fantastic Four” reboot this weekend, they’ll likely assume that it’s the third entry in the cinematic superhero saga. But a new documentary hopes to dispel that myth once and for all.

“Doomed: The Untold Story of Roger Corman’s The Fantastic Four” reveals the baffling circumstances that led to the filming of an unreleased 1994 feature film starring Marvel’s comic book quartet that was never meant to be seen publicly.

The story goes like this: In late 1992, three years after the success of Tim Burton’s “Batman,” producer Bernd Eichinger approached low-budget filmmaking maestro Roger Corman about making a movie based on the Fantastic Four. Eichinger, the German producer of “The Neverending Story,” had acquired rights to the superhero team’s story and needed to begin production immediately.

In short order, a professional cast and crew was assembled, sets and costumes were constructed and filming began at Corman’s Venice Beach studios and around Los Angeles. The speed of the production was extreme even by Corman’s standards, but the filmmakers believed this would be a major theatrical release and their efforts would be worth it.

The first hint of trouble came when Marvel’s Stan Lee was asked at a 1993 comic book convention about what he thought of the film in production.

“I don’t think much of it,” Lee commented dryly.

Principal photography wrapped in a speedy 28 days, but the film languished much longer in post-production, without any sign that the producers intended to actually finish it. Hoping to salvage their work, director Oley Sassone and editor Glenn Garland struggled to complete the movie in secret by borrowing rolls of film and cutting new footage on the sly.

The cast hired a publicist at their own expense to help promote the film, and a major public screening was eventually scheduled in 1994 at the Minnesota’s Mall of America. That premiere was cancelled at the last second, however, when the actors received a cease and desist order from the producers.

Virtually overnight, the 35mm negatives were confiscated and the film, much like the Invisible Girl herself, vanished. In time, the truth began to emerge. This version of “The Fantastic Four” wasn’t supposed to see the light of day. The plan was to purposefully shelve it from the very beginning.

The deal between Marvel and Eichinger’s Constantin Films was a purely contractual issue that allowed the producers to extend their option on the source material at a very low cost — as long as production began by December 31, 1992, after which Constantin would lose the rights. Corman himself may have been duped to some extent.

The cast and crew were stunned by the betrayal. They’d joined the project in good faith, but all the time and energy they’d invested was now pointless. Roger Corman’s “The Fantastic Four” was a lie that just happened to be filmed, and remains unreleased to this day. Although trailers were shown at conventions in 1993, the movie itself never arrived — Marvel exec Avi Arad had bought the film to prevent it being released and has said he had the negatives destroyed.

Marty Langford, the director and editor of “Doomed,” first learned of its existence in a 1993 issue of Film Threat magazine. “They ran an amazing cover story with the cast in full costume,” he said. “That was when my excitement really began.”

Eventually, a grainy bootleg copy of “The Fantastic Four” was leaked and began circulating among fans. Due to its extreme low budget and rushed shooting schedule, the film itself is often barely competent. Yet those limitations give it a cheesy charm all its own.

“I always thought there was a much bigger story there somewhere,” Langford said. “So after waiting 15 years for someone else to tell it, I decided to do it myself.”

As luck would have it, Langford’s childhood friend Mark Sikes was the casting assistant on the Corman film, and joined the documentary as executive producer. “Mark still had the original sign-in sheets for all the actors who auditioned for it,” Langford said. This included current Avenger Mark Ruffalo, who auditioned for the role of Dr. Doom.

Gathering the original cast proved easier than expected. “They were anxious to tell their story,” Langford said. “But it became clear during our interviews that some of them hadn’t completely healed from what happened back then.”

With the Fox reboot opening Friday, Marvel is taking a hands-off approach to the documentary. “We kept expecting they would sue us at some point, but it didn’t happen,” said Langford.

Langford and Sikes even reached out to Lee, who declined to be interviewed for their film. “They know we exist, but they’re taking the same stance that Disney took with ‘Escape From Tomorrow’ by ignoring us.”

The documentary, which American Cinematheque is screening in Los Angeles on Aug. 13, is distributed by Uncork’d Entertainment. An eventual Blu-ray, VOD and limited theatrical release is planned to coincide with the reboot’s video release sometime in January.

Langford’s ultimate goal is larger than his own film finding an audience, however. “Our hope is that all of this attention might convince Marvel that the market is more than ready for the original Fantastic Four movie to finally come out.”