"I was at home and I got a phone call," he said on the Jonathan Ross Show. "It was early in the morning. I was in the country and I just got a phone call. I think it was like that for everyone, just so horrific, you couldn't take it in. And I couldn't take it in."
For lack of better words, McCartney said the man who took Lennon's life -- Chapman -- all he could think was "jerk of all jerks."
"He's just a jerk. It's not even a guy politically motivated," he added. "Just some total random thing."
McCartney added that he's glad that after the band broke up in 1970, he was able to reconnect with Lennon before he died.
"I'm so glad because it would have been the worst thing in the world to have this great relationship that then soured and he gets killed, so there was some solace in the fact that we got back together. We were good friends," the iconic musician said on the show, according to People.