"I was singing Here Today for John, which is always such an emotional song because it brings back memories of me and John when were kids," the Mirror quoted McCartney as telling a fans' question and answer session in Montreal, Canada.
"I was holding it together until I saw a girl in the audience had totally lost it and was weeping. And it got me. I tried to look away, but it was impossible," he added.
And he revealed that his most memorable gig so far was when he played for President Obama in the White House earlier this year.