The star was at a live event at London's Southbank Centre where he was interviewed on stage to promote new book The Lyrics about his career in The Beatles and beyond.
According to Metro, he said of his close friendship with the late Lennon and telling him how he felt: "You know, as 16-year-old, 17-year-old Liverpool kids, you could never say that, it just wasn’t done. So I never did.
"I never really just said: 'John, love you man.' I never got around to it.
"So now it’s just great to realise how much I love this man."
Talking about how special it was to work with Lennon, Sir Paul made it clear he was in awe of his friend's talent, adding that "you are not just singing with Joe Bloggs. You are singing with John Lennon" as he tried to explain the significance of their time together.
Sir Paul, who has also recently spoken about clearing up rumours over who was responsible for calling time on The Beatles, said during the interview that the biggest misconception about him was that he had ended the band rather than Lennon.
Fans had mistakenly thought that he had broken up the group, a rumour that Sir Paul said he "lived with for quite a while" and admitted it was something "I’ve only finally just got over".
Recently, Sir Paul told Reader's Digest that he wouldn't sign any more fan autographs and preferred people to have a chat with him instead of asking for selfies.
He said: "It always struck me as a bit strange – 'here, can I write your name down on the back of this till receipt please?' Why? We both know who I am.
"What you've usually got is a ropey photo with a poor backdrop and me looking a bit miserable. Let's chat, let's exchange stories."
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