The breakup of the Beatles wasn’t the friendliest of splits, with John Lennon channelling his acrimony toward songwriting partner Paul McCartney in some particularly savage songs.

In People‘s excerpt from McCartney’s new book, Lyrics: 1956 to the Present, McCartney opens up about his fractious relationship with Lennon during the fraught period after the split.

“When we broke up and everyone was now flailing around, John turned nasty. I don’t really understand why. Maybe because we grew up in Liverpool, where it was always good to get in the first punch of a fight,” McCartney writes.

READ MORE: Paul McCartney Reflects On John Lennon’s Death, Mending Their Friendship

“John was firing missiles at me with his songs, and one or two of them were quite cruel. I don’t know what he hoped to gain, other than punching me in the face. The whole thing really annoyed me,” McCartney recalled.

“John would say things like, ‘It was rubbish. The Beatles were crap.’ Also, ‘I don’t believe in the Beatles, I don’t believe in Jesus, I don’t believe in God.’ Those were quite hurtful barbs to be flinging around and I was the person they were being flung at, and it hurt. So, I’m having to read all this stuff, and on the one hand I’m thinking, ‘Oh f— off, you f—ing idiot,’ but on the other hand I’m thinking, Why would you say that? Are you annoyed at me or are you jealous or what? And thinking back 50 years later, I still wonder how he must have felt,” McCartney adds.

“How Do You Sleep?”, from Lennon’s solo debut John Lennon/Plastic Ono Band, was unmistakably a musical insult directed at McCartney. “The sound you make is muzak to my ears/You must have learned something in all those years,” Lennon sings, while another verse states: “The only thing you done was yesterday/And since you’re gone you’re just another day.”

McCartney fired back, but his musical responses were far more subtle. “I decided to turn my missiles on him too, but I’m not really that kind of writer, so it was quite veiled,” he explains. “It was the 1970s equivalent of what we might today call a ‘diss track.’ Songs like this, where you’re calling someone out on their behaviour, are quite commonplace now, but back then it was a fairly new ‘genre.'”

One such song was McCartney’s “Too Many People” from his Ram album, with the line, “You took your lucky break and broke it in two,” directed at Lennon. “[That] was me saying basically, ‘You’ve made this break, so good luck with it.’ But it was pretty mild… It was all a bit weird and a bit nasty, and I was basically saying, ‘Let’s be sensible. We had a lot going for us in the Beatles, and what actually split us up is the business stuff, and that’s pretty pathetic really, so let’s try and be peaceful. Let’s maybe give peace a chance.'”

READ MORE: Sir Paul McCartney Says He Was ‘So Happy’ To Reunite With John Lennon Before His Death

Over the years, however, McCartney could feel Lennon softening.

“At first, after the breakup of the Beatles, we had no contact, but there were various things we needed to talk about,” writes McCartney. “Our relationship was a bit fraught sometimes because we were discussing business, and we would sometimes insult each other on the phone. But gradually we got past that, and if I was in New York I would ring up and say, ‘Do you fancy a cup of tea?'”

That thawing increased after Lennon and wife Yoko Ono welcomed son Sean in 1975. “We had even more in common, and we’d often talk about being parents,” McCartney divulged.

When Lennon was assassinated by Mark David Chapman in 1980, the former bandmates were on the path to resparking their friendship.

“I was very glad of how we got along in those last few years, that I had some really good times with him before he was murdered,” McCartney writes. “Without question, it would have been the worst thing in the world for me, had he been killed, when we still had a bad relationship. I would’ve thought, Oh, I should’ve, I should’ve, I should’ve… It would have been a big guilt trip for me. But luckily, our last meeting was very friendly. We talked about how to bake bread.”

READ MORE: Paul McCartney Still Hasn’t Gotten Over John Lennon’s Murder: ‘It Was Just So Senseless’

According to McCartney, Lennon’s influence continues to be present in his songwriting.

“As I continue to write my own songs, I’m still very conscious that I don’t have him around, but I still have him whispering in my ear after all these years,” McCartney explains. “I’m often second-guessing what John would have thought — ‘This is too soppy’ — or what he would have said different, so I sometimes change it. But that’s what being a songwriter is about; you have to be able to look over your own shoulder…Now that John is gone, I can’t sit around sighing for the old days. I can’t sit around wishing he was still here. Not only can I not replace him, but I don’t need to, in some profound sense.”