12-Minute Acoustic Song by Kurt Cobain to Appear in HBO Doc

A decade ago, some of Kurt Cobain's archival material was included on the Nirvana box set With the Lights Out. That compilation wasn't entirely exhaustive, since the soundtrack of the new documentary Kurt Cobain: Montage of Heck has also promised "previously unheard Cobain originals." We now know that one of those will include a previously unheard 12-minute acoustic song from the iconic grunge songwriter.

This news was revealed by Montage of Heck director Brett Morgan, who tweeted on Saturday (March 7) that this "acoustic" track is "mind-blowing." He described it as a Cobain song, rather than Nirvana, so we're guessing that the rest of the band aren't involved.

Listening to a mind blowing 12 minute acoustic Cobain unheard track that will be heard on the montage of heck soundtrack. Hello @truefalse

— Brett Morgen (@brettmorgen) March 7, 2015

While we'll have to wait to hear that track, we can be fairly certain that the film won't include "Flaccid Bone," a fake Nirvana song that recently popped up online. TMZ reported that Cobain's widow Courtney Love is apparently working with law enforcement to try to track down the perpetrator, who falsely claimed that he had hacked Love's computer for the song. Hear the song below; it's a halfway-decent imitation, but it's not likely to fool many fans.

Montage of Heck will premiere on HBO on May 4. It has already premiered at film festivals. A companion book will be out on April 7 through Insight Editions. Judging by Morgan's tweet, there's going to be a soundtrack album too.