Kanye West and Paul McCartney have very different writing processes, apparently. In an interview with DIY, McCartney recalls writing “FourFiveSeconds” as “much more made up as we went along” compared to what he’s used to, “so much so that I didn’t even realize that I was making songs.” The two spent a few afternoons together in the bungalows of a Beverly Hills hotel, surrounded by microphones and Kanye’s engineer “incase anything happened.”

“I was tootling around on guitar, and Kanye spent a lot of time just looking at pictures of Kim on his computer. I’m thinking, are we ever gonna get around to writing?! But it turns out he was writing,” McCartney explains. “That’s his muse. He was listening to this riff I was doing and obviously he knew in his mind that he could use that, so he took it, sped it up and then somehow he got Rihanna to sing on it.”

Elsewhere in the interview, McCartney discusses his role on Kanye’s “All Day.” He was surprised to learn he had worked on a song with Kendrick Lamar after looking up the song’s writing credits. “There’s about 50 people! There were only three of them I knew and one of them’s Kendrick Lamar! I’m thinking, I’ve written a song with Kendrick Lamar?! I wish I’d met him,” he says. David Longstreth of Dirty Projectors is another secret Kanye-collaborator McCartney was excited to hear about. McCartney read that his “latest claim to fame was that he wrote the middle eight for ‘FourFiveSeconds.’”

As for Kanye’s discography, McCartney is a fan of My Beautiful Dark Twisted Fantasy. He also likes Watch The Throne, which he calls “urban poetry.” Overall, he feels “lucky” to be working with the younger generation of hitmakers.