The musicians bonded over the losses of their mothers and that served as inspiration for West's own music. "We sat around and talked an awful lot just to break the ice," he said in an interview with The Sun, via Rolling Stone. "One of the stories I told him was about how I happened to have written 'Let It Be'," he said, sharing that "Let It Be" and its back story served as an inspiration for "Only One."
He recalled an anecdote he shared with the rapper. "My mum came to me in a dream when she'd died years previously. I was in a bit of a state - it was the Sixties and I was overdoing it. In the dream she said, 'Don't worry it's all going to be fine, just let it be.' And I woke up and thought, 'Woah' and wrote the song... [Kanye] said, 'I'm going to write a song with my mum.' So then I sat down at the piano."
McCartney also shared that the sessions reminded the former Beatle of another person he used to work with -- John Lennon. McCartney elaborated on working with the rapper and how it wad a callback to his process with Lennon.
"When I wrote with John, he would sit down with a guitar. I would sit down. We'd ping-pong till we had a song," McCartney said "[Working with West] was like that."
Not only did the the guys craft "Only One," but also worked together -- along with Rihanna-- on "FourFiveSeconds."
"My first thought was, 'Woah, what am I going to get into here,'" he said. "He is amazingly talented but controversial and can make eccentric moves. I realized if it didn't work out we'd just say so and shake hands and leave."