“This is Spinal Tap” director, Rob Reiner, reflected on how misunderstood the mockumentary was when it first came out 41 years ago.

“Initially, it didn’t catch on right away,” he shared in an exclusive interview with Page Six. “The audience didn’t immediately grasp the concept. They assumed it was an actual documentary about a legitimate band. After the first screening, people approached me saying, ‘I’m confused. Why create a film about a band that’s completely unknown?'”

The 1984 comedy features Reiner as Martin DeBergi, a director making a rock documentary about a fictitious British heavy metal band named Spinal Tap as they embark on an ill-fated US tour. It also stars Christopher Guest, Michael McKean and Harry Shearer as the band members.

In fact, the movie was so misunderstood that the “Princess Bride” director had a hard time getting even producers interested in it.

“We tried for years,” he recalled. “We went around with this 20-minute demo reel that we had and nobody wanted it. Everybody passed on it. Nobody understood it.”

Finally, they found executives who believed in the project and managed to secure financing from Reiner’s old “All in the Family” boss, Norman Lear.

“He took a big leap of faith,” Reiner noted. “He was my champion, my whole career.”

Despite the audience’s initial apprehension, the comedy became a cult favorite, even among real rock stars.

“I remember when I ran into Sting the first time,” Reiner recalled. “He said to me, ‘I’ve seen this movie over and over. Every time I watch it, I don’t know whether to laugh or cry.’ So, I mean you know, we obviously touched a nerve.”

The film is also now in the National Film Registry at the Library of Congress, and the Oxford English Dictionary has an entry for the movie’s iconic quote, “goes to 11,” that’s “used not just for the loudness of rock and roll music, but you know, anything in excess.”

To celebrate its 41st anniversary, the movie will be shown on screens across the country from July 5-7.