On Friday, November 5, the "Yesterday" hitmaker appeared at the Royal Festival Hall in London for his first live event in two years and discussed his new book with poet Paul Muldoon, "The Lyrics: 1956 to the Present", about the inspiration for some of his best-loved songs.
He fondly remembered how his life changed when he met up with the rest of The Fab Four - especially John.
"The four of us miraculously found each other," he said, explaining he and Lennon, who was shot and killed in 1980, shared a deep connection.
"It's like walking up a staircase and we've always been side by side on that staircase. I'm like a fan. I just remember how great it was to work with him and how great he was. Because you are not just messing around, you are not singing with Joe Bloggs, you are singing with John Lennon."
But Macca still has one huge regret now his pal is no longer around - he never told John he loved him.
"As 17-year-old Liverpool kids you could never say that. It just wasn't done," he shared.
"So I never really said, 'John, love you mate.' I never got around to it, so now it's great to know how much I love this man."