There's one very memorable scene in HBO's new Kurt Cobain documentary

After receiving three Emmy nominations following its airing on HBO in May, "Kurt Cobain: Montage of Heck" is back in theaters Friday.

The documentary has a treasure trove of never-before-seen material that looks back on the childhood and private life of the legendary lead singer of Nirvana, who tragically took his own life in April 1994 at the age of 27.

But there's one particular piece in the film, 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.

Surprised to find the box, as no one told him any audio was stored there, Morgen tracked down a few cassette decks and began transferring them into digital files.

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.

And the 2007 film, "Chicago 10" - a look at the anti-war protestors put on trial following the 1968 Democratic National Convention - is entirely animated.

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."

Morgen asked Hulsing to join the project to animate the Cobain audio story. Hulsing also animated another audio sequence later on in the film in which Cobain is recording the mundane moments of his life while living at his girlfriend's house in the '80s.

"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.

Morgen played Hulsing an edited version of the audio that was more polished and streamlined than the original recording he discovered in the cardboard box. Morgen also came up with a shot list for Hulsing to follow while making the animation, and the two went back and forth for months on storyboards.

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 also on 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 it to Morgen back in L.A. for approval.

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

Below is an excerpt from Cobain's audio story in "Kurt Cobain: Montage of Heck," accompanied by select GIFs of Hulsing's animation from the sequence in the film.

Trevor was a guy I hated but resorted to becoming friends with because he was the only person I could get pot from. He was the kingpin. Trevor, Ace, John, Darin, all white-trash low-life scum of the earth, according to the jocks. They had been going to this girl's house after school and they invited me. We got to the door and a very fat girl let us in.

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.

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.

But nothing ever mattered. I decided within the next month I would not sit on my roof and think about jumping but I'll actually kill myself. And I wasn't going out of this world without actually knowing what it was like to get laid.

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---."

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.

And that day the girl's father came in screaming and accusing someone of taking advantage of his daughter. And so during lunch rumors started and by the next day everyone was waiting for me to yell and cuss and spit at me, calling me "the retard f----r."

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.

And the train came closer, and closer, and closer and went on the next track besides me. And it stood over me over.

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."

Hulsing also said that Cobain's blank facial features in the story came from how he and Morgen believed Kurt felt in his social setting. "He's hanging out with a group he's not a real part of," he said. "Kurt's own voiceover already explains his own state of mind as a teenager, the way he felt rejected and ridiculed, I didn't want to overdo that."

There were also some visuals that don't match what Cobain says, particularly the line when he goes to the railroad tracks to commit suicide: "Put two big pieces of cement on my chest and legs and waited for the eleven o'clock train." According to Morgen, that was intentional. "I decided to take that one moment and deviate from Kurt's narrative just a bit to kind of embrace the subjectivity of the sequencing and acknowledging that we are interpreting these events," he said.

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."

Looking back on making the film, Morgen said Hulsing's work was always the wild card.

"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."

What's fascinating to learn about Cobain's audio story is that it may not be true.

"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 in April.

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."