Dave Grohl doesn’t believe anyone will figure out the identity of the “biggest pop star in the world” who makes a guest appearance on upcoming Foo Fighters album Concrete and Gold. And while he’s offered more hints about the person involved, he also says he should never have spoken up in the first place.

The follow-up to 2014’s Sonic Highways is released Sept. 15 after the band cut short a planned year-long hiatus to return to work. Produced by Greg Kurstin, best known for his work with pop stars Adele, Kelly Clarkson and others, Grohl has described the LP as a blend of “the love of ‘70s AM gold radio and the love of Motorhead.”

The bandleader first hinted in June that an unexpected icon had played a part, saying: “[He or she] sings backup on one of the heaviest songs on the record – and we’re not telling anyone who it is.” He later discounted Adele and Taylor Swift. In a new interview Grohl told Rolling Stone, “I’d be amazed if anyone can really figure it out. But it was great. This person’s been around a long time.

“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. [He or she] is very talented – more so than I ever knew. But of course, I 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!’”

Discussing how the collaboration came about, he said, “It was towards the end of the album and this person came up and said, ‘Man, I’d really love to sing on your record.’ I looked at Greg and said, ‘Okay, come in tomorrow and we’ll figure something out.’ We found a backup part and we decided we were gonna make it our own dirty little secret and see if anyone can figure it out.”

He added that the artist in question was one of the people he’d asked to appear in the second season of his Sonic Highways documentary series, which originally accompanied the album of the same name. Reflecting that he’d love to work with both Adele and Swift, Grohl added: “Maybe everyone should just start submitting their wish list and then the next album will be We Are the World. We could do this.”

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