Stockman: Gilbert Carrasquillo/Getty Images; Grohl: Harry Durrant/Getty Images

Visiting BBC 6 Music's morning show on Thursday, Foo FightersDave Grohl dropped a tidbit about Concrete and Gold. The frontman previously teased the upcoming album as featuring "probably the biggest pop star in the world, and I’m not kidding," and now we know what that means to Grohl. It's Shawn Stockman, of Boyz II Men.

Asked what the "weirdest moment" making the band's ninth album was, Grohl said:

“The guy from Boyz II Men walking through the parking lot and me saying ‘Oh, dude, will you sing on our record?’ And he does. On the heaviest song on the entire record. It sounds like Sabbath and Pink Floyd made their—it’s the last song on the record. [Shawn is] singing like a choir, he built a choir, it’s like 40 vocals stacked. It’s insane, it's amazing.”

Grohl said the song, also Concrete and Gold's title track, concludes a theme worked through in the prior 10 cuts, making it "kind of the resolve of the entire record." The disc will feature the band finding, after years of trying, its #weirdalbum sweet spot. “It is the record that I’ve been more excited for people to hear than any other record we’ve ever made,” Grohl said.

Foo Fighters premiered a new track, "Dirty Water," earlier this week in Paris. Concrete and Gold drops Sept. 15, accompanied by a personalized festival and a big tour.

Watch an in-depth Foos x Fuse interview: