Here's the moment HBO knew its Scientology doc 'Going Clear' would be a huge hit

Although the HBO documentary "Going Clear: Scientology and the Prison of Belief" is one of the most-watched docs in the history of the network, the head of HBO Documentary Films, Sheila Nevins, didn't think a scathing look at the Church of Scientology would draw a lot of viewers when director Alex Gibney initially pitched her the idea.

"I never thought it would be sensational," Nevins told Business Insider.

Before Gibney went to her, Nevins said she had never considered doing a film on the religion. She gave the go-ahead because she had confidence that the Oscar-winning Gibney ("Taxi to the Dark Side," 2007) could pull off a great adaptation of best-selling author Lawrence Wright's book on the church, "Going Clear: Scientology, Hollywood, and the Prison of Belief."

Nevins remembers the exact moment when she realized "Going Clear" was going to be a huge hit. "When I saw my name in a full page ad in The New York Times, I knew," she said. "Docs don't get full page ads, and when they do, they do really well."

Nevins is referring to the ad that Scientology ran in The Times weeks before the film had its world premiere at the Sundance Film Festival in January.

The ad compared "Going Clear" to the now infamous Rolling Stone story on campus rape at the University of Virginia, which turned out to be full of false claims. The headline in the ad read, "Is Alex Gibney's Upcoming HBO 'Documentary' a Rolling Stone/UVA Redux?"

The ad then went on to outline numerous instances in which the church believed "Going Clear" was not factually correct.

It also stated: "Mr. Gibney and HBO documentary chief Sheila Nevins have rejected multiple requests to meet with executives of the Church, including those with individual firsthand information."

"I thought, 'They really don't want us to do it,'" said Nevins. "All the reason more to do it."

Nevins told The Hollywood Reporter months before the film premiered at Sundance that "probably 160 lawyers" were vetting the film.

Gibney told Business Insider by email that the legal process with HBO was "tough but fair," and he couldn't have imagined bringing the project anywhere else other than to HBO.

"They were fearless and supportive," he wrote. "Sheila and HBO backed me up against the attacks we knew were coming and promoted the hell out of the movie."

Thinking back on the whole ordeal, Nevins still can't believe the church was so aggressive in trying to bash "Going Clear."

"Scientology did their own commercial for us," she said. "Going Clear" had its premiere airing on HBO in March and became the second most-watched documentary on the network in the past decade.