Love, the widow of Nirvana frontman Kurt Cobain, and Frances, their daughter and an executive producer on the film, have had a rocky relationship but presented a united front on the red carpet Friday.
The film, directed by Brett Morgen, is the first authorized film about Cobain. Morgen says it took eight years to make it happen, six of which were just spent licensing material. The last two was what he calls "aggressive filmmaking."
"There were serious doubts along the way," said Morgen. "This film challenged me. It took everything I had to sort of get it here. There's a lot of pressure of getting it right and it's a very unorthodox film.
Among the rare material Morgen was able to use in the film was footage of Cobain performing the Beatles song, "And I Loved Her", original never-before-heard recordings and home video of him and Love.
The director says he finished color correcting the movie less than a week ago, and when he was finished he "went to the bathroom and cried for about 25 minutes."
"I wasn't crying because Kurt died," he said. "I was crying because I wasn't going to be able to spend time with him anymore. And for the last two years he's been everything in my life."
Morgen believes fans will perhaps understand the musician more after seeing "Cobain: Montage of Heck."
"A man emerged that was romantic and funny and warm and (with) issues and whatnot. I don't want to paint a ... perfect (picture). It's a complicated story. I think part of a thing with this film is it has all of it."
The movie premieres on May 4 on HBO.