Nirvana producer Butch Vig reveals that despite the seemingly endless stream of exhaustive box sets and rarities collections that have been unfurled over the last decade, there's still one unreleased Nirvana track that remains in the band's vault. It's titled simply, 'Song in D.'

If true, the tune -- an instrumental track (as in, it has no lyrics!) that one would assume was recorded in the always-popular 'drop D' tuning -- would be the first previously unheard Nirvana song to drop since 'You Know You're Right,' the last song Nirvana recorded, surfaced in 2002.

Even with the slew of posthumous Nirvana releases ('Nirvana,' With the Lights Out,' 'Sliver: The Best of the Box,' 'Icon' and more) featuring tons of rarities, demos, outtakes and live recordings, 'You Know You're Right' remains the one true new posthumous track from the band.

Vig revealed this information during a recent two-hour Q&A session with Dave Grohl and Krist Novoselic that was hosted by comedian Jon Stewart. That discussion aired via SiriusXM radio on Saturday, which was the 20th anniversary of the release of Nirvana's watershed 'Nevermind' album. Upon hearing Vig's claim, Grohl, ever the witty one, declared, “Sounds like another box set!”

Loudwire recently feted two decades of 'Nevermind' with the special feature, 20 Things You Didn't Know About Nirvana's 'Nevermind.' How many those 20 did you already know? Check it out here and tell us your score. Also, enter below for a chance to win a copy of the deluxe 20th anniversary edition of 'Nevermind.'

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