Upon the announcement of the band's upcoming album Concrete and Gold, Foo Fighters frontman Dave Grohl hinted that one of the world's biggest pop stars was making a guest appearance on the disc, but he's managed to keep that secret under wraps so far. Even so, he did offer some more fuel to the fire, while also eliminating to big names.

"We decided we were gonna make it our own dirty little secret and see if anyone can figure it out,” said Grohl to Rolling Stone about the mystery guest making an appearance on their latest album. "[He or she] sings backup on one of the heaviest songs on the record," he added. "And we're not telling anybody who it is."

Grohl declined to reveal the mystery superstar's name, but he did provided a few more hints, walking back the "pop star" comment he made originally. "This person is, I think, is more than that," he says. "It was sort of towards the end of the album and this person came up and said, 'Man, I'd really love to sing on your record,'" Grohl says. "I looked at [producer] Greg [Kurstin] and said, 'OK, come in tomorrow and we'll figure something out.' So we found a backup part for this person to sing.”

"I'd be amazed if anyone can really figure it out," he says. "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------ fun. And [he or she is] very talented – more so than I ever knew. But, of course, I f------ 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.'"

His final hint was that the person was someone with whom he'd talked to about doing the next season of his TV series Sonic Highways. "Everyone thinks Adele sang on the record," he says. "She didn't sing on the record. I f------ love her, she's an amazing person – I love her personally, and I of course also love her music – but I think everyone made this correlation because Greg had produced her. I'm like, 'F---, I wish it was Adele. Godd--n, that'd be amazing.'"

He also declined the idea that Taylor Swift was a potential guest. "Ooooh, that'd be a good one," he says. "Wasn't T-Swift. She's pretty rad, but... That's the thing. Maybe everyone should just start submitting their wish list and then the next album will be 'We Are the World.' We could do this."  Some of the guests that Grohl did confirm as having made an appearance on the record include the Bird and the Bee's Inara George, who sings on "Dirty Water." Grohl’s good friend, Dave Koz, plays on "La Dee Da" and the Kills' Alison Mosshart sang on "La Dee Da" as well as "The Sky Is a Neighborhood.”

One of the other highlights for Grohl was asking Boyz II Men singer Shawn Stockman, whom Grohl had spotted in the parking lot, to create a choir for the song "Concrete and Gold." "When he left the room, I turned to everybody and I said, 'You guys, the Boyz II Men dude just raised the f------ bar. Every song has to sound this big," Grohl said.

Concrete and Gold is the upcoming ninth studio album for Foo Fighters. It is scheduled for release on Sept. 15 of this year. The album's first single, "Run", was released in June.

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