Brett Morgen, the director of the upcoming Kurt Cobain documentary Montage of Heck, tweeted on March 7 (as Loudwire points out) that there will be a 12-minute, acoustic track from the late Nirvana frontman that has never been released. Morgen said, “listening to a mind-blowing 12-minute acoustic Cobain unheard track that will be heard on the Montage of Heck soundtrack.”

While no other details were revealed, Morgen has previously confirmed to Rolling Stone that the documentary’s score will feature all unreleased music from Cobain, which includes a snippet of The Beatles’ “And I Love Her” that Morgen found on a tape. “Nobody in Kurt’s life–not his management, wife, bandmates–had ever heard this,” he said.

Montage of Heck will premiere on HBO on May 4 and the film’s companion book featuring a rare photos and other memorabilia from Cobain’s life will be released April 7.