The cause was cancer, according to a statement on her son Julian Lennon's website.
Cynthia and John Lennon met at the Liverpool College of Art in the late 1950s. "He was always around, always surrounded by people who were in awe of him," she said in a 1995 London Times interview. "He was embarrassingly funny, and you couldn't resist it."
Author Hunter Davies, who wrote the only authorized Beatles biography in 1968, described her as "quiet and reserved and calm." He said their friends at art school never thought the relationship would last because they were so different.
But they married in 1962, when she was pregnant with Julian. It was the same year the Beatles made their first single, "Love Me Do."
Cynthia Lennon has been portrayed as wanting only a simple, domestic life, but she said in a 1995 interview with the Independent in London that that was far from the truth.
"I was training as an art teacher for four years, and it was only when I became pregnant that marriage followed, and the Beatles followed after that," she said.
She was born Cynthia Lillian Powell on Sept. 10, 1939, in Blackpool, England. She grew up in the seaside town of Hoylake, where she was a soloist in the local girls' choir but wanted to pursue a career in art. She enrolled in the art college in nearby Liverpool in 1957.
Beatles manager Brian Epstein wanted the couple to keep their marriage secret, believing it would be better if fans thought the Fab Four all were single. But as the group shot to fame, it was inevitable word would get out. When the Beatles made their live American TV debut in 1964 on "The
But Cynthia Lennon didn't take well to the trappings of rock star life. "The first thing to do is if you're a pop star and you get a lot of money, you buy a mansion," she said on the public radio show "Fresh Air" in 2010. "All of a sudden, you find yourself with a chauffeur and a housekeeper and a cook and an interior designer and all the things in life that you've never experienced before."
Meanwhile, she and her husband were drifting apart. Besides his all-consuming life as a Beatle, he was experimenting with drugs and had multiple affairs. The marriage finally came apart when she came home from a trip to find artist Yoko Ono dressed in her bathrobe in the house.
After the 1968 divorce — in which she got custody of Julian, the house and 100,000 pounds (about $240,000 at the time) — Cynthia Lennon tried many endeavors. She was a TV host, recorded a song, sold much of her memorabilia and wrote two memoirs.
She ended her 2005 book, "John," saying she was grateful for her son. But she wrote, "If I'd known as a teenager what falling for John Lennon would lead to, I would have turned round right then and walked away."
John Lennon was killed by an assassin in 1980. Cynthia Lennon had four marriages — her last, to Noel Charles, ended with his death in 2013. She is survived by her son.