There is a very special guest on the upcoming Foo Fighters album.

In June, during an interview with BBC Radio 1, Dave Grohl teased that the band’s new album, “Concrete and Gold”, has one surprise feature that he isn’t revealing.

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“There’s one who is probably the biggest pop star in the world. He or she sings backup on one of the heaviest songs on the record. And we’re not telling anybody who it is,” Grohl teased.

"The biggest pop star in the world" features on the new @FooFighters album 🤔 Dave Grohl tells @AnnieMac all about new music & Glastonbury! pic.twitter.com/WA6ZozxRi9 — BBC Radio 1 (@BBCR1) June 20, 2017

Now, while Grohl isn’t revealing who that feature may be, ET Canada learned of another feature on the album.

We got to sit down with the Foo Fighters and Grohl revealed to us who one of the surprise guests on the album is: Paul McCartney.

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“Paul McCartney plays drums on one of our songs. He’s a pal. We’ve known him for a long. He’s great. He’s the most wonderful person in the world. He’s a great guy,” Grohl said.

“He hadn’t even heard of the song. He comes in and Dave picked up an acoustic and showed him real quick. He sat on his special drum set that his tech set up for him. I sat there with a drumstick conducting. He did two takes,” the band spilled to ET Canada.

In an interview with Rolling Stone, Grohl explained how the special feature which he still won’t reveal the name of came about. “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 admitted.

“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 and we decided we were gonna make it our own dirty little secret and see if anyone can figure it out,” he continued.

We’ll have to wait and find out when “Concrete and Gold” is released on September 15.