Paul McCartney has quite the discography, but it's The Beatles' final song "Now and Then" that makes him "very emotional" when he plays it live.
“It’s really great. When you introduce a new song, even though it’s an old song, like ‘Now and Then’, the first reaction is, people aren’t quite sure what it is or what you’re doing," Macca explained in an interview with the Mirror. “But during the run of the concerts, they get the idea. The word gets out on the internet, you know. So now the reaction is really strong, and for us it’s great to play because it’s a nice song to play, and for me, it’s particularly great because it’s a John song. And so it’s very emotional for me. I love it. I love doing it, and the audience seems to love it too.”
"Now and Then" was originally recorded as a demo by John Lennon in 1977, features guitar recorded by George Harrison in 1995, and was finished by McCartney and Ringo Starr in 2022. McCartney first performed the song live on October 1 during a concert in Uruguay.
Macca is currently on tour in the UK and a fan got footage of him visibly emotional after playing the song. You can watch that and listen to "Now and Then" below.