US -FILM-PREMIERE-FANTASTIC FOURA scathing new report about the filming of "Fantastic Four" has provided some insight into how and why the underwhelming film -- which was widely panned and majorly flopped at the box office -- turned out the way it did, and it seems that the flick was a disaster from the start.

The Hollywood Reporter did some digging and spoke to several sources about the allegedly arduous production process, and it turns out that the rumors of director Josh Trank being difficult to work with were just the tip of the iceberg. According to one crew member who spoke to THR, Trank "built a black tent around his monitor" and would hole up in there or in his trailer alone for entire shooting days, emerging only to film a scene.

The director reportedly insisted on pushing "a gloomy tone" on the cast (Miles Teller, Michael B. Jordan, Kate Mara, and Jamie Bell), and was "telling [castmembers] when to blink and when to breathe," an insider told THR.

"[M]ultiple sources associated with the project say the director did not produce material that would have opened the way to a salvageable film," THR wrote. "And by several accounts, he resisted help."

Eventually, talk turned to firing Trank, but a source told THR that that suggestion came too late in the production process, and would have required essentially scrapping the entire movie and losing the cast -- a huge financial blow. Instead, studio Fox enlisted producers Simon Kinberg and Hutch Parker to slap together a different ending, and commissioned reshoots without key actors (only Teller was available, and shot scenes on a green screen alongside body doubles). Director Drew Goddard was reportedly brought in to supervise.

"It was chaos," according to one crew member.

But the blame doesn't stop there. Per THR:

A crewmember acknowledges that Trank bears much of the fault for the film's problems but also says the Fox studio should not escape blame. The movie was "ill-conceived, made for the wrong reasons and there was no vision behind the property," this person says. "Say what you will about Marvel but they have a vision."

Yowza. Check out the rest of the blistering report over at THR.

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