When Beatlemania broke in 1963 journalists approached Cynthia, though her friends and neighbours tried to protect her. In December she had Julian christened without John Lennon's knowledge, which angered him. Shortly afterwards news of Cynthia and Julian appeared in the national press, putting an end to their anonymity.
They moved first to a flat in Emperor's Gate, London, though attention from fans made life difficult. It became harder when she went with The Beatles on their first trip to America. In New York she was left behind when the band were swept away in a car, and in Miami she was held back by a disbelieving security guard. Lennon's reported response was: "Don't be so bloody slow next time - they could have killed you".
With The Beatles' fame becoming intense, the Lennons relocated to the stockbroker belt in Surrey, buying a mock-Tudor house in Weybridge called Kenwood for £20,000.
In the beginning when we go the flat in London then we were totally unprotected and we had no idea what was going to happen at all. We couldn't get in or get out of the flat and I used to get some terrible funny phone calls and I had a weirdo at the door one day when I was on my own with Julian. So it was decided that the only way to escape that was to get out and into the country.
Cynthia was given a £50 allowance each week, with which she enjoyed shopping and spending on the family. She became close to Ringo Starr's wife Maureen, and George Harrison's wife Pattie. The Lennons also enjoyed London's nightlife, and attended film premières and special events.
In March 1965 the Lennons and the Harrisons were unwittingly introduced to LSD after their coffee was spiked at a dinner party. Although John found the experience fascinating, Cynthia described it as "horrific". With John's encouragement she reluctantly took it again on two further occasions, though he was a much more enthusiastic advocate of the drug.
Lennon's infatuation with LSD during 1966 and 1967 caused a gradual rift in their relationship. When she was left behind on the station platform in Bangor, Wales, where The Beatles had gone to see the Maharishi Mahesh Yogi, she described it as symbolising their marriage: Lennon was heading off into the future while she remained on her own.
When Cynthia flew to India to meditate with the Maharishi in February 1968, she felt the gap growing further between her and John. When they returned, he confessed that there had been a stream of other women, including Joan Baez and journalist Maureen Cleave, and thousands of groupies around the world. He claimed that he had been unfaithful from their days together at college. Cynthia was stoic in her response; she had long suspected Lennon's infidelity, but had become adept at ignoring it.
Lennon encouraged Cynthia to holiday in Greece while he was recording the White Album. While she was away he began a physical relationship with Ono. Cynthia returned to find Ono wearing her bathrobe, drinking tea with her husband. Lennon's response upon seeing her was: "Oh, hi".
Cynthia spent the night with Pattie Harrison's sister Jenny Boyd, and Alexis Mardas, a friend of the band known as Magic Alex. Mardas got Cynthia drunk and tried to sleep with her. Later, on a holiday in Italy with her mother, Mardas appeared and informed Cynthia that Lennon was divorcing her on the grounds of adultery.
The mere fact that Magic Alex arrived in Italy in the middle of the night without any prior knowledge of where I was staying made me extremely suspicious. I was being coerced into making it easy for Lennon and Yoko to accuse me of doing something that would make them not look so bad.
Cynthia returned to Kenwood with Julian, and Lennon and Ono first set up home together in Ringo Starr's flat in London. They had a brief meeting again, where Lennon accused her of an affair in India, saying she was far from an "innocent little flower".
She refused to claim half of his fortune, choosing to avoid a lengthy court process. Lennon initially refused to give Cynthia more than £75,000, saying "That's like winning the pools, so what are you moaning about? You're not worth any more." She later accepted £100,000, plus £2,400 in maintenance, custody of Julian and ownership of Kenwood. The divorce was finalised on 8 November 1968.
Earlier that year Paul McCartney had visited Cynthia and Julian at Kenwood, despite Lennon's objections. On the way there he began composing Hey Jude, addressing it to Julian. He gave Cynthia a red rose, and joked: "How about it, Cyn? How about you and me getting married now?" She was touched by his gesture, and never forgot it.
After divorcing Lennon, she remarried three times, and in 1978 published her autobiography, A Twist Of Lennon, which detailed her life with John. She published a new biography of him, titled John, in September 2005.
Cynthia was told about John Lennon's death by Ringo Starr, who phoned her in London from America.
I don't remember getting out of bed and going down the stairs to the phone. But Ringo's words, the sound of his tearful voice crackling over the transatlantic line, is crystal clear: 'Cynthia, I'm so sorry, John's dead.' In my stunned state I had only one clear thought. My son - our son - was at home in bed. I had to get back to Ruthin so that I could tell him about his father's death.