Courtney Love used heroin while pregnant.

The 50-year-old star took the Class A substance while she was expecting her and the late singer Kurt Cobain's daughter Frances Cobain, who is now 22, but she was confident doing the drug wouldn't harm her unborn child.

Speaking in documentary film 'Kurt Cobain: Montage of Heck', Courtney says: ''I used it once then stopped. I knew she would be fine.''

The documentary tells the story of the Nirvana frontman's early years up until his success and downfall with the grunge group as well the struggles Kurt - who committed suicide in 1994 - had with becoming a parent.

Speaking about Frances, he says in archive footage: ''I don't want her to be screwed up.''

The singer also discusses his quest to be a better father than his dad Donald, who re-married after splitting from the star's mother Wendy, much to the rocker's dismay.

He says: ''My father and I are very different people, I am capable of a lot more affection than he is.''

While there is no drug use shown in the film, Courtney claims her late husband just wanted to ''stay in their apartment, do heroin and paint'' when he decided he had had enough of the limelight with Nirvana.

Courtney and Frances were seen in public together for the first time in five years on Saturday (24.01.15) at the 2015 Sundance Film Festival, where they embraced each other on the red carpet before watching the documentary.