Here's how one of the most memorable scenes from HBO's Kurt Cobain documentary was made

But there's one particular piece in the documentary, directed by Brett Morgen ("The Kid Stays in the Picture") that no one, not even Cobain's family or closest friends, ever knew existed.

Morgen had been working on the project for five years when he finally got the call. In 2013, he was granted access to a storage space where Cobain's most intimate materials - journals he wrote and paintings he created - are kept.

"One of the things that would change the direction of the film was a box that I found that said, 'cassettes,'" Morgen told Business Insider.

Hidden among the hours of recordings of Cobain playing music and joking around, he came across a story Cobain taped in 1988.

"I knew instantly it was different because he was performing it and was doing multiple takes on it," Morgen explained. "It was a little more narrative than most of Kurt's art."

The story Cobain tells in the recording is of his first sexual encounter, which then leads to the first time he contemplated suicide.

Morgen brought the recording to the Cobain family, who had never heard it. He even brought it to the attention of Cobain's biographer, Charles R. Cross, who wasn't aware of its existence, either.

Morgen knew it needed to be in the film, but how could he make it work visually for the movie?

Morgen is famously known for using animation in his work. In "The Kid Stays in the Picture," he used effects to bring still photography to life in his story of Hollywood mogul Robert Evans.

But Morgen admits he initially had no intention of animating the Cobain audio.

"We were going to animate his art and his journals (made for the film by artist Stefan Nadelman), but there was never a discussion about animating Kurt," he said.

But then he came across the work of Dutch artist/filmmaker Hisko Hulsing and his animated film, "Junkyard."

"I felt that he had a similar dystopian view of the world that Kurt had, but a much better craftsman than Kurt," said Morgen of Hulsing. "But the view and the tone had a lot of similarities, a lot of darkness and twisted reality."

"I've never been a Nirvana fan," Hulsing admits. "I think I was 21 when 'Smells Like Teen Spirit' became a hit and I just had a dark, psychotic adolescence, so it didn't strike a right cord for me."

But Hulsing said he agreed to come on because he was fascinated by Morgen's mission to celebrate Cobain's life, not mythologize his death.

From his small studio in Amsterdam, Hulsing compiled a team of 27 people (18 of them animators) and for four months they worked on not only the Cobain audio story, but the other portion of the film Hulsing was responsible for. For the 85 shots that were Hulsing's responsibility, they produced 6,000 animations and 60 oil paintings on canvas. Some of those canvas paintings were as large as six feet.

Hulsing would then take a digital picture of the canvas, input the animation that would go in front of it, and send to Morgen back in L.A. for approval.

Here's an animated rendition of Cobain as a teenager.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"It wasn't obvious to me for over an hour that this girl seemed kind of quiet until one of the guys pointed out that she was in a Special Ed class. I'm sure a lot of kids would call her a retard and some just slow, and at the time, and still to this day, I would call her quiet and illiterate. But not retarded.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"The object of the guys who'd been going there for the past month was to steal booze from the downstairs basement of her house. While others distracted her, one would go down and take a fifth and then exit the downstairs. We did this routine every other day and got away with it for, oh, about a month.

And during that month happened to be the epitome of my mental abuse from my mother. It turned out that pot didn't help me escape my troubles too well anymore, and I was actually enjoying doing rebellious things like stealing booze and busting store windows.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"So one day after school I went to the girl's house alone and invited myself in and she offered me some Twinkies and I sat on her lap and I said, "Let's f---."

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"And I touched her and she went into her bedroom and got undressed in front of me and I watched and actually realized it was actually happening. So I tried to f--- her but didn't know how, so I asked her if she'd done this before and she said, a lot of times, mainly with her cousin.

I got grossed out very heavily with her smell and her sweat reeked, so I left. My conscious grew to where I couldn't go to school for a week and when I did I got in-house suspension for skipping.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"I couldn't handle the ridicule. So I got high and drunk, I walked down to the train tracks and laid down and put two big pieces of cement on my chest and legs and waited for the eleven o'clock train.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"And the train came closer, and closer, and closer and went on the next track besides me. And it stood over me over.

HBO/Hisko Hulsing/"Kurt Cobain: Montage of Heck"Detention from school had an effect on me, and the train scared me enough to try to rehabilitate myself by lifting weights and mathematics seemed to be improving so I became less manically depressed. I still didn't have any friends because I hated everyone for they were so phony.

Hulsing said the bleak look he gave the animation came from what he observed looking at photos of Aberdeen, Washington, where Cobain grew up.

"Images and videos of Aberdeen clearly show that it's often grey and rainy," Hulsing said. "I believe that the somber palette adds a lot of darkness and hopelessness to the story of young, suicidal Kurt."

The music played over the telling of the story is a string arrangement of the Nirvana hit, "Smells Like Teen Spirit," arranged by composer Jeff Danna. "There was already some existing music of strings playing 'Smells Like Teen Spirit,'" Hulsing said. "So [Morgen] put that under my moving storyboards in the beginning and it really worked for Brett, so later he had a new composition done."

"Once we saw the final assembly edit, Joe Beshenkovsky, who edited the film with me, both of us felt we were pretty comfortable where we landed," said Morgen. "But at the same time we knew Hisko was just getting started [on animating]. There was this fear, 'Hisko is going to be our Achilles heel if he doesn't deliver.' It's not like we could cut out the sequence. I've had some treacherous experiences with animation not really working out the way you'd hoped."

But when Hulsing delivered the first drawings, all the anxiety rushed away.

"He gave me a gift," Morgen said. "He was really committed to the work. He really wanted to get it right and I really appreciate that about him."

Hulsing said with a chuckle about the experience, "I'm still recovering."

"I met Krist Novoselic, the bass player for Nirvana, at Sundance and he said that he knew Kurt very well from a young age and he never heard that story before," said Hulsing.

Morgen and Cobain's wife, Courtney Love, also questioned the story's veracity at a Q&A following the film's screening at the Tribeca Film Festival last month.

But, Morgen told BI, whether it's real or not doesn't interest him.

"I'm not a writer or a historian," he said. "I'm making a movie and it's a depiction of his art, so I'm out for an emotional truth."

NOW WATCH: New HBO documentary reveals what controversial singer Kurt Cobain was really like