Dave Grohl teases fans with mystery guest on 'Concrete and Gold'
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Dave Grohl and the Foo Fighters have a “dirty little secret” and so far they’re holding their cards close to their chest as to just who the megastar mystery singer is on their forthcoming album, Concrete and Gold. As Rolling Stone reported, Grohl recently told BBC Radio 1 that the “biggest pop star in the world” sang backup vocals on one of the album’s tracks but that they’re “not telling anybody who it is.” Grohl did, however, leave a few more clues for curious fans.

Related: Foo Fighters debut new song, 'Dirty Water'

Grohl modified his “biggest pop star in the world” comment saying that the person was “more than that.” He also stated that this person had “been around a long time” and that he had approached them about working on his ongoing TV series "Sonic Highways." That was about it for the hints, but Grohl did mention a few big names who were not on the album, including Adele and Taylor Swift. Concrete and Gold comes out Sept., maybe then we will know the megastar's identity.

The Foo Fighters will be performing at London's O2 Arena on Sept. 19. Click here for tickets.