Foo Fighters will release their new album 'Concrete & Gold' this September, and it looks like Dave Grohl and his bandmates may have a few tricks up their sleeve for it.

Grohl - who headlines Glastonbury this weekend with the band - told BBC Radio 1's Annie Mac that it would be very different sort of album to 2014's 'Sonic Highways', and that it will feature 'numerous guests', including 'some that will really surprise you."

He continued: "There’s one who is probably the biggest pop star in the world and -- I’m not kidding -- sings backup on one of the heaviest songs on the record, and we're not telling anybody who it is.”

Needless to say, that teaser has led to feverish speculation on who he might be talking about, with many pointing immediately to Adele. Grohl has publicly praised the Londoner in the past, and they share a producer in Greg Kurstin, who oversaw Adele's '25'.

Other names in the frame include Beyoncé, Taylor Swift and Katy Perry (both of whom also have connections with the band via Kurstin) and the less likely Justin Bieber and Ed Sheeran.

The album's out on September 15th, so there's only a few months to wait to find out...