Sir Paul McCartney opened up about his experience of collaborating with Kanye West for their hit song “FourFiveSeconds” and revealed the rapper’s unique writing process.

McCartney told DIY he let West “lead the dance” on the hit 2015 song that featured Rihanna.

“We ended up just talking a lot,” McCartney told DIY. “I played a few little things and one of them ended up as ‘FourFiveSeconds’ with Rihanna. It’s more a question of me feeling lucky that these people are interested [in working with me] and think that I can bring something to it. For me, I feel great. I like diversity.”

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McCartney said he “learned a lot” while collaborating with West and described the inspiration behind West's lyrics.

The Beatles singer said he would write songs by sitting down “with a guitar or at a piano and make it up and complete it."

Paul McCartney said Kanye West would look at photos of Kim Kardashian while writing songs. (Reuters)

And West would make up the song “as we went along – so much so that I didn’t even realize that I was making songs," McCartney added.

“We had two or three afternoons where we just hung out together in a Beverly Hills hotel in the bungalows out the back, and he had his engineer and was set up with a couple of microphones in case anything happened,” he said. “I was tootling around on guitar, and Kanye spent a lot of time just looking at pictures of Kim [Kardashian] on his computer. I’m thinking, ‘Are we ever gonna get around to writing?'"

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McCartney, 76, said he was surprised to learn West was writing.

“But it turns out he was writing. 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. She’s a big favorite of mine anyway so that just came without me lifting a finger,” he explained.

The former Beatle announced on Wednesday that his 17th solo album, “Egypt Station,” will be released on Sept. 7. He released the singles “I Don’t Know” and “Come On To Me.” His last album, “NEW,” is from 2013.