Nirvana frontman Kurt Cobain's demo version of the band's popular hit "Sappy" has been released online.

The track, which is a rough recording of the single "Verse Chorus Verse," was unveiled in a puzzle game from the official website of the documentary "Kurt Cobain: Montage of Heck."

The puzzle game also revealed the cover for the new posthumous solo album from the late rocker called "Montage of Heck: The Home Recordings," according to Spin.

The album will be released on Nov. 13 and will serve as the official soundtrack to the HBO documentary about Cobain.

Additionally, "Montage of Heck: The Home Recordings" will also include a cover version made by Cobain of the Beatles song "And I Love Her," according to Times of India.

These recordings made by the rocker, who died on April 5, 1994, were discovered by Brett Morgen, who serves as the director of the documentary, according to Slate.

Listen to the audio recording of "Sappy" below: