Sir Paul McCartney is one of the most successful and beloved musicians of all time, and also one of the most famous celebrity animal rights activists.

So it’s no surprise that sometimes, his love for songwriting and animals come together in the best ways — including one classic Beatles tune that might sound like a traditional love song, but is actually about Paul’s pet dog!

Paul’s sheepdog

1965 was a major year for The Beatles. Continuing their reign as the biggest music act in the world, they released hit albums Help! and Rubber Soul while embarking on their first US tour.

It was also a major personal year for Paul, who purchased a new home on Cavendish Avenue in London, where he would compose some of the Beatles’ greatest songs.

And to keep him company, he also bought an Old English Sheepdog puppy whom he named Martha.

Martha became one of his most beloved companions, bringing out a joyous side of him his bandmates had never seen before.

“She was a dear pet of mine,” McCartney once said, per the Liverpool Echo. “I remember John being amazed to see me being so loving to an animal. He said, ‘I’ve never seen you like that before.’ I’ve since thought, you know, he wouldn’t have.”

“It’s only when you’re cuddling around with a dog that you’re in that mode, and she was a very cuddly dog.”

“Martha My Dear”

And Paul’s love for his dog is immortalized in a Beatles tune he named after her: “Martha My Dear.”

The memorable tune was part of the Beatles’ landmark self-titled 1968 album, better known as The White Album. At first listen, it’s easy to mistake it for being a love song about a human woman named Martha: “Martha, my love, don’t forget me.”

But Paul has confirmed that “Martha My Dear” was in fact inspired by his sheepdog. And if you look closer at the lyrics, it starts to make sense:

Hold your head up, you silly girl
Look what you’ve done
When you find yourself in the thick of it
Help yourself to a bit of what is all around you
Silly girl

In his book The Lyrics, McCartney said he wrote the song while challenging himself to write a complex piano composition, challenging his skills.