Upon learning she was pregnant, John decided they should get married and the couple tied the knot shortly before their son was born.
Around Cynthia’s due date, The Beatles were on tour, meaning the Imagine hitmaker missed the birth of his first child, business coming first.
She gave birth to Julian in a private room at Sefton General Hospital for the birth, paid for by the band’s manager Brian Epstein.
It was three days later that John finally met his son. John’s incredible first words to Julian would, remarkably, turn out to predict the course of his life after The Beatles icon’s death.
In How’s Your Dad?: Living in the Shadow of a Rock Star Parent, author Zoë Howe reveals the first words The Beatles star said to his newborn son.
Arriving at the hospital three days after Julian was born, he picked up his baby son and said: “Who’s going to be a famous little rocker like his dad then?”
As an adult, Julian launched a musical career, following in his famous father’s footsteps.
He never reached the lofty heights of The Beatles, but has had varying success over the years, releasing his debut album in 1984, four years after John’s death.
While his dad was alive, their relationship was complex, the musician being largely absent during Julian’s childhood.
The Beatles were at the peak of their popularity, with Beatlemania sweeping the world, and John’s relationship with his first wife Cynthia began to break down in the years after Julian was born.
Then, in 1966, her husband met avant-garde artist Yoko Ono.
Though they were both married at the time, they began corresponding, but it wasn’t until two years later that what had blossomed into a romance between John and Yoko proved the final straw for his marriage to Cynthia.
The mother-of-one returned home from a holiday with Julian to find John and Yoko sat on the floor of the home she shared with him, having spent the night together, a moment she later said effectively put an end to the marriage for everyone involved.
Cynthia and John were divorced later that year and she got full custody of Julian.
The Beatles star married Yoko the following year and, shortly afterwards, he left the band and moved to New York with his new wife.
While John was living in New York, he saw relatively little of Julian but they reconnected in 1973 during the musician’s ‘lost weekend’ — the 18 months he spent in an affair with May Pang and living in Los Angeles.
It was then Julian would visit his father regularly and they bonded with John encouraging his interest in music and helping introduce him to the guitar.
In 1980, several years after returning to Yoko in New York, John was fatally shot outside their home.
In a 1998 interview with The Telegraph, Julian vented his anger towards his “hypocrite” dad and the way he handled the break-up of his first family.
“From my point of view, I felt he was a hypocrite,” he said. “Dad could talk about peace and love out loud to the world but he could never show it to the people who supposedly meant the most to him: his wife and son.
“How can you talk about peace and love and have a family in bits and pieces — no communication, adultery, divorce?” he added.
Over a decade later, however, Julian revealed his bitterness towards his father had changed over time.
“With Dad running off and divorcing Mum, I had a lot of bitterness and anger I was living with,” he told CBS. “In the past, I had said I had forgiven Dad but it was only words.
“I realised if I continued to feel that anger and bitterness towards my dad, I would have a constant cloud hanging over my head my whole life.”