The Beatles icon Paul McCartney has revealed the one song that never fails to make him "break down in tears".

Despite penning classics such as Hey Jude, Band on the Run, and Get Back, it's a tune from one of his 1960s rivals that moves him to tears every time he hears it. The Beatles' star labelled the song as one of his all-time favourites, recounting an instance when he broke down in front of the original songwriter during a rehearsal of the track.

McCartney's fans have been left debating the collaborative effort, expressing their wish for more than just a handful of rare performances. A thread on Reddit saw listeners reminiscing about a 2002 rendition of the song. One user questioned why McCartney and The Beach Boys' Brian Wilson hadn't collaborated in the studio, with many pointing to a poignant moment which brought Sir Paul to tears.

One fan queried: "I've always found it perplexing who McCartney chooses to collaborate with. Very few were of this calibre but I wonder why he's never cowrote anything with Brian Wilson. Any thoughts?"

Another responded: "Although not a writing collaboration, Paul has spent time in the studio with Brian. He allegedly has an uncredited performance on the celery of The Beach Boys' delightfully weird Vegetables."

McCartney's studio cameo on a lesser-known Beach Boys tune has stirred whispers, but it's his teary-eyed experience with "God Only Knows' that has left fans moved. Sir Paul counts the Beach Boys classic as one of his dearest tracks.

A fan reminisced: "He's definitely a fan. Has said God Only Knows is one of his favorite songs and he has appeared on stage with Brian to sing it at a benefit in LA in 2002."

McCartney himself has spoken on how "God Only Knows' is one of the few songs that reduces me to tears every time I hear it. It's really just a love song, but it's brilliantly done. It shows the genius of Brian. I have actually performed it with him."

He said: "God Only Knows' is one of the few songs that reduces me to tears every time I hear it. It's really just a love song, but it's brilliantly done. It shows the genius of Brian. I have actually performed it with him.

"And I'm afraid to say that during the soundcheck, I broke down. It was just too much to stand there singing this song that does my head in and to stand there singing it with Brian."

Additionally, McCartney expressed admiration for George Harrison's songwriting skills, with "Brainwashed" earning a spot among his favored tunes.

He fondly recalled Harrison, saying, "Didn't suffer fools gladly," and described him as a "lovely man, I love him dearly, I grew up with him, and I like to remember all the good times.

"Fantastic guy, with a great sense of humor. I was lucky enough to see him a couple of weeks ago, and he was still laughing and joking."