A new documentary is blowing the lid off history’s most famous Bigfoot sighting, exposing the legendary footage as a hoax with a newly unearthed “rehearsal” reel.

The film, “Capturing Bigfoot,” which hits theaters and Prime Video on Oct. 20, features a top-secret canister of 16mm film stashed away in a safe for decades, showing a “test run” clip of the hairy guy, purportedly shot in 1966 — exactly one year before Roger Patterson and Bob Gimlin’s famous film tricked the world.

The shaky footage is 40-seconds long and shows a Bigfoot walking through the woods and looking over its right shoulder in a very similar manner to Patterson-Gimlin’s footage, which they said was taken in Bluff Creek, Calif., on Oct. 20, 1967.

The 1967 footage is widely considered by enthusiasts and researchers as the definitive evidence of the creature’s existence.

The new footage is shot in a lush forest with a more svelte, ape-like creature retreating into the woods slowly, distinct from the Patterson-Gimlin film, which showed the Bigfoot stalking through leafless stretch of woods.

“This is like the Holy Grail or something. This is going to change everything about my dad’s film,” Roger Patterson’s son Clint says in “Capturing Bigfoot.”

Both films were shot on the same K-100 Kodak film camera, which left a unique edge, numbers and geometric designs date codes on the film itself.

“That’s the answer we’ve been looking for, for years. That’s definitely faked and that’s definitely rehearsed,” said Larry Lund, known as the “Sasquatch Sleuth,” after being shown the film.

“So uncannily like the ’67 film. To me it’s a practice,” said Greg Long, author of “The Making of Bigfoot.”

“It’s a smoking gun, and thank God someone’s found it,” he added.

The bombshell reel was discovered in 2017 by Teresa Brooks, the daughter of Norm Johnson, who worked in the film department of Boeing in the 1960s. Brooks, a professor at Olympic College in Washington state, then gave the footage to her colleague, filmmaker Marq Evans.

Johnson was recruited into Roger Patterson’s hoaxing plot, but never spoke out publicly due to pressure from his wife, Brooks claimed in the doc. She came into possession of the film reel after her mother died in 2017.

“This film has been sitting in a safe for 50 years,” Brooks said in the film. “Part of me wanted to keep the family secret.”

Lund’s emotional reaction to finding out the original footage was a hoax was featured in the documentary.

“I feel a deep loss,” he said. “Look what he’s done to people. The lives he changed,” the 80-year-old sasquatch seeker said, shaking his head.

Lund’s friend Rene Dahinden, one of the first Bigfoot hunters who was obsessed with the original Patterson-Gimlin film, lost his marriage and his family and died alone because of his dedication to the search.

Clint Patterson revealed in the film that his mother Patty confirmed to him that Bob Heironomus, who has long claimed to be the person in the suit in the 1967 video, was part of the hoax.

“That means my dad lied to me,” Patterson said, choking back tears. “He was my hero.”

Patty allegedly cut-off contact with Clint after he expressed a desire to come forward with the truth. Clint has remained silent for the last eight years because the rights of the Patterson-Gimlin footage are his mother’s sole source of income, he claimed in the documentary.

“I don’t like being a liar. And I’m ready to come clean,” said Patterson.