Billboard reports the film's return to theaters on August 7 will see the soundtrack include the untitled song, which features Cobain singing in a falsetto.

The period of the demo's recording is unknown because it was pulled from an unmarked cassette, but Morgen says there's some evidence that Cobain recorded it in 1991 because it appears on a tape "on which he was also working on 'Old Age,'" which was written during the "Nevermind" sessions.

Morgen says he inserted the new song without altering the cut of the movie that played on HBO, which has since been nominated for seven Emmys.

He declined to divulge where the track appears "because I don't want to get people out there bootlegging it on their cell phones." Read more and check out the trailer - here.

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