For well over 20 years, it's been rumored that Courtney Love used heroin while pregnant with Kurt Cobain's daughter, Frances Bean Cobain. The story has become part of Nirvana folklore, but in the new documentary 'Kurt Cobain: Montage of Heck,' Love finally admitted that the rumors were true.

'Kurt Cobain: Montage of Heck' just had its inaugural screening at the 2015 Sundance Film Festival. The doc will be broadcast by HBO on May 4, but we've got details about the film which will keep you salivating for the next few months.

First of all, Nirvana drummer / Foo Fighters frontman Dave Grohl was strangely absent from the Kurt Cobain film. This was due to editing issues, as the filmmakers were unable to insert Grohl into 'Montage of Heck' in time for Sundance. However, director Brett Morgan hopes to get Grohl into the flick in time for its HBO premiere.

Courtney Love actually got the ball rolling for 'Kurt Cobain: Montage of Heck' back in 2007, while Frances Bean Cobain served as executive producer. According to MTV, mother and daughter reunited for the first time in five years while walking the Sundance carpet. The two embraced at the event, but a dark reality awaited viewers once 'Montage of Heck' began to roll.

In the film, Love spoke about using heroin during her pregnancy with Frances. “I used it once then stopped,” Love said. “I knew she would be fine.” Footage of Kurt Cobain also documents the musician's own contemplations of fatherhood. “My father and I are very different people, I am capable of a lot more affection than he is,” Cobain said. “I don’t want her [Frances Bean] to be screwed up.”

Be sure to catch 'Kurt Cobain: Montage of Heck' once it debuts on May 4 via HBO.

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