Dave Grohl of Foo Fighters has opened up about their mystery collaborator on their forthcoming album 'Concrete And Gold'. Having previously teased that it was a huge popstar, he has finally admitted that Justin Timberlake lent his vocals to one track on the new record.

Foo Fighters to release new album 'Concrete and Gold'Foo Fighters to release new album 'Concrete and Gold'

The 36-year-old singer didn't have more lyrics than 'la la la' on the title track, but the collaboration came about when he was hanging out with the band in between recording sessions at L.A.'s EastWest studios. It was really a last minute decision for the group.

'We'd drink whiskey in the parking lot', Dave told Rolling Stone. 'He was really, really cool. Then the night before his last day, he says, 'Can I sing on your record? I don't want to push it, but - I just want to be able to tell my friends.''

The frontman had only really mentioned that it was a major pop star on one of the heaviest tracks previously, but that was enough to have people asking him exactly who it was non-stop. Thus, he had to reveal the secret to avoid the frantic speculation.

'I'd be amazed if anyone can really figure it out', he said at the time. 'But it was great and this person's been around a long time. And I think I've met this person maybe a few times, but I'd never spent time with this person, and we had a blast together. Really f***ing fun. And very talented - more so than I ever knew. But, of course, I f***ing ran my mouth off; now I have to answer to it every time I pick up the telephone and I'm like, 'F***! I shouldn't have said anything.''

Another big name cameo on the Foo Fighters' ninth album is Paul McCartney who plays drums on the song 'Sunday Rain', Bird and the Bee's Inara George on 'Dirty Water', the Kills' Alison Mosshart on 'La Dee Da' and 'The Sky Is a Neighborhood', and Boyz II Men's Shawn Stockman on 'Concrete and Gold'.

More: Foo Fighters release new song 'The Sky Is A Neighborhood'

'Concrete and Gold' will be released on September 15th 2017.