Foo Fighters will release their new album Concrete and Gold on September 15, an album that features a number of unique guests including Boyz II Men’s Shawn Stockman as well as Paul McCartney and Justin Timberlake, whose appearance Dave Grohl teased as “the biggest pop star in the world.”

As for Timberlake’s appearance, Grohl spoke with Rolling Stone in a wide-ranging interview that touched on their meeting.

“We’d drink whiskey in the parking lot,” Grohl said of his interaction with Timberlake. “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.’”

Timberlake added some background vocals to a track before departing. “He nailed it,” Grohl said.

For McCartney’s part, the band asked him to play drums on a track to which the famed Beatle responded, “You’re crazy, man.”

“Even if it had been banjo, I think I probably would have showed up,” McCartney said, who has previously jammed with Grohl as a part of his Sound City documentary. The likes of which turned into a mini-Nirvana reunion with Krist Novoselic, Grohl and Pat Smear.

“It’s inspiring,” Grohl said. “Because he’s still playing for the same reasons we all started playing when we were young. He just wants to jam.”

Foo Fighters’ drummer Taylor Hawkins applauded McCartney’s drum chops, saying “he laid that track so fucking effortlessly. He never even heard the song [before].” Grohl agrees, “He was so fucking good.”

As for the Foo Fighters’ upcoming one-day festival Cal Jam, where they recruited close friends (“drinking buddies” as Grohl says) Queens of the Stone Age, Liam Gallagher, Cage the Elephant and others, Grohl mentioned that they had originally booked Soundgarden prior to Chris Cornell’s death.

“It didn’t happen,” an emotional Grohl explained. “He was a really sweet guy. Full of life. And he had so much to offer. That one hurt,” he said of Cornell. “I felt for his family and I felt for his band, you know? Because that’s a long road, man.”

Read the full interview here.