The 74-year-old musician doesn't think he will ever get on so well with another collaborator again as he did with the late musician, reported Rolling Stone magazine.
"I don't think it could be. At some point, you have to realise, some things just can't be. John and me, we were kids growing up together, in the same environment with the same influences. He knows the records I know, I know the records he knows. You're writing your first little innocent songs together. Then you're writing something that gets recorded," McCartney said.