During an interview Ed Sheeran discussed what he and his multi-time collaborator Eminem bonded over to wind up having a “cool pen-pal thing.”

During an interview on the BBC’s Later…with Jools Holland, Ed Sheeran opened up about his friendship with multi-time collaborator Eminem, revealing their bond stems from a mutual love for collecting old cassette tapes.

“I collect cassettes, and I’ve got Ray Charles and Stevie Wonder, and they are quite difficult to find,” Sheeran said. “The only person I know who collects the same is Eminem. He collects cassettes, that’s his thing. He loves collecting. He is avid at going to find them. We have started having this, it’s like a very cool pen-pal thing.”

The pop singer-songwriter continued, “I got a message the other day from Marshall about an LL Cool J cassette. He said, ‘This is the cassette which made me want to start rapping.’ I sent him Van Morrison and I will send him David Gray’s White Ladder next.”

Their love for collecting cassettes isn’t the only thing the co-creators of “River,” “Remember the Name,” and “Those Kinda Nights” have in common. While speaking with Apple Music back in August, Sheeran shared a story about a studio session with Eminem, which was highlighted by a four-hour conversation about their Marvel fandom.

“The first time we met, we didn’t make music,” he said. “I hung out there for about four hours and we just spoke Marvel and Avengers for about four hours. And then the next time I went back, we made a tune. The first tune we made, I was in Mexico and his producer flew to Mexico and I did the hook there and stuff.”