Producter Butch Vig, who helped bring forth the best of the guitar crunch, Cobain shrieks and shattering backbone that made Nirvana's seminal album Nevermind a modern classic, announced via Twitter that he was collaborating again with the other two-thirds of Nirvana, Dave Grohl and Krist Novoselic: "The last 24 hours have been surreal! Had a great gig at the El Rey last night, and spent today recording with Dave, Krist and special guest!" [Insert weak joke about the guest being Hologram Kurt Cobain here.]

This isn't the first time Butch Vig has reunited with Messrs. Grohl and Novoselic. Vig produced the Foo Fighters' most recent album, Wasting Light, and Novoselic appeared as a guest star on track "I Should Have Known."

It's not clear who the mystery guest is or what the reunion is for, but Consequence of Sound suggests it could be for the upcoming Grohl-helmed documetary Sound City, about the iconic studios where Nevermind and Fleetwood Mac's Rumours were recorded and featuring interviews with Trent Reznor, Stevie Nicks, Tom Petty and members of Ratt.

Watch the trailer for Sound City, featuring a whole lot of famous musicians and with a release date to be determined, below:

<iframe src="http://player.vimeo.com/video/36565630?title=0&amp;byline=0&amp;portrait=0&amp;color=ffffff" width="400" height="225" frameborder="0" webkitAllowFullScreen mozallowfullscreen allowFullScreen></iframe><p><a href="http://vimeo.com/36565630">Sound City - A film by Dave Grohl</a> from <a href="http://vimeo.com/soundcitymovie">Sound City</a> on <a href="http://vimeo.com">Vimeo</a>.</p>