In 2014, Paul McCartney received an unexpected message: Kanye West was interested in writing music with him. McCartney agreed even though he was unsure of what awaited him.

The pair met for a couple of afternoons in Los Angeles, and McCartney quickly discovered that his interpretation of a writing session differed from West's. They spent most of the time talking.

"I had my bass ready in case we were going to get more serious," McCartney later told GQ. "I thought we might actually sit down and write a song in the way I was used to writing a song — actually craft something there and then. It turned out we were creating an 'ingredient pool,' which is how he does it."

That "ingredient pool" eventually included additional vocals from another unexpected source: Rihanna. Although West's style of music-making was a bit puzzling to McCartney, the resulting track, "FourFiveSeconds," became his biggest hit in decades. It debuted on the Billboard Hot 100 chart at No. 54 but within weeks shot to No. 4.

"If I want to go somewhere else from where I normally go or where I'm expected to go, I'll go. And if I enjoy it, that's enough for me," McCartney said. "The great thing is, all sorts of hysterical things come out of it. I mean, there's a lot of people who think Kanye discovered me. And that's not a joke."

You can learn more about this collaboration in the below video from our "Odd Couples" series.

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