McCartney was devastated when he discovered his longterm songwriting partner had been murdered outside his New York City apartment by Mark David Chapman on 8 December 1980 - but now chooses to focus on the good times they shared together.
The 63-year-old tells BBC Radio 2, "The first thing that goes through your mind is the horrific conditions of his death. That's what always hits me. And you think, 'Gosh, my mate, that's what happened to him.'
"But then, rather than dwell on that, I immediately go to the fantastic times we had and how lucky and privileged I feel to be one of the people who spent the most time with him during his life having met him as a teenager.
"People start these rumours: 'He was this, he was that.' I say, 'Look, I've slept with him.' We've done hitch-hiking holidays and we've had to top and tail it because there was only one bed. I say, 'I knew him'.
"The bottom line, I think what everybody already knows, he was a fantastic man, really fantastic guy.
"Just as a man, as an activist, he is one of the great men of the 20th century. I'm just very proud to have known him so intimately from when we were kids to virtually the end all the way through."