JOHN Lennon is remembered for his soft-spoken messages of peace and love – but the beloved Beatle had a hair-trigger temper so volatile, nearly anything could set him off. And one night, it exploded in an incident that ended up damaging his son’s hearing.

In a jaw-dropping postscript in Philip Norman‘s new biography, “John Lennon: The Life,” out next month, Sean Lennon tells how his father flew off the handle and screamed into his ear as a young boy.

“[He was] teaching me how to cut and eat steak, which was a mystery to me at age 4; how to stick the fork in and cut behind it, and that was how you got a piece in your mouth,” writes Sean, 32, whose mom is Yoko Ono. “I think it was that night when he got very upset with me, I think because of something I did very cheekily with the steak. He did wind up yelling at me very, very loudly to the point where he damaged my ear, and I had to go to the hospital.”

He says John, mortified by his cruelty, was immediately apologetic: “I remember when I was lying on the floor and hurting, and him holding me and saying, ‘I’m so sorry.’ He did have a temper.”

Sean recalls his dad’s soft side, too. “I remember one time he accidentally let one of the heavy wooden doors at The Dakota slam on my finger,” Sean tells Norman. “And he was very upset about that. My fingernail eventually fell off.” Another time, “Alice, our black cat, had jumped out the window after a pigeon and died, and I remember that was the only time, I think, I ever saw my dad cry.”

Of Lennon’s leaving the Fab Four to form the Plastic Ono Band with Yoko, “that to me was like when Matisse turned his back on painting and decided that everything he wanted to say artistically from now on could be said by a few simple shapes cut out of paper. It was as if Elvis had left Vegas in the ’70s and started to play with the punks.”