Courtney Love admits using heroin during pregnancy in Kurt Cobain documentary

PARK CITY, Utah – "KURT COBAIN: Montage of Heck" is the first family-authorized documentary about the life of late "Nirvana" front man Kurt Cobain, taking audiences inside the mind of the troubled and talented musician.

"In 2007 got a call from Courtney [Love, his wife] who wanted a film that went beyond the music. The journey started there. But I made this for Frances [Bean Cobain, the couple’s daughter]. She gave me the keys to go and make the film," director Brett Morgen told FOX411. "If you come to the movie thinking that you are going to see the story of Nirvana, you are only going to be sorely disappointed. This is the Kurt Cobain story."

Bean, 22 served as executive producer on the film, offering up very personal Super 8 footage of her early months being raised by rock star parents devoted to their daughter while struggling with drug addiction. At one point in the film, Love admits that she used heroin while pregnant.

"I used it once then stopped," Love said. "I knew she would be fine."

Much of the documentary examines Cobain's struggle with parenting and the drive to be the father he never had in his life.

"My father and I are very different people, I am capable of a lot more affection than he is," Cobain states in archival footage. "I don't want her to be screwed up."

"Montage of Heck" also functions as something of a love story, first of all detailing Cobain’s relationship with live-in girlfriend Tracy while he was working as a janitor in Seattle after dropping out of school, and then his roller coaster relationship with Love.

"Kurt was romantic and goofy and funny, he was not a whiny rock star. He was truly, genuinely in love with Courtney in a way that contributed to his death," Morgen explained. "He felt things more intensely than most people. People are going to see that when Kurt wasn't on stage, he was a completely different person."

According to Love, at the height of Nirvana's fame Cobain chose to withdraw from the limelight, wanting only to "stay in their apartment, do heroin and paint." While actual drug use is not shown, Cobain's descent into addiction becomes increasingly evident. He committed suicide in 1994.

"This is a psychological portrait of Kurt. I didn't sugarcoat anything, he was a junkie," Morgen said. "This is a difficult film for his family. Of course I could have been more sensitive, but I always thought the person I had to be most sensitive to was Kurt. I had to put him first.”

The film did manage to reunite Love and her estranged daughter at the Sundance Film Festival premiere in Park City, Utah over the weekend.

"So sad yet so uplifting, beautiful and gorgeous. Your daddy would be so proud of you baby," Love tweeted, referring to their daughter. "Thank you."