John Lennon's first wife Cynthia died today at her home in Spain with her son Julian by her bedside, her family said.
A message on Julian's website said she died "following a short but brave battle with cancer".
It said: "Her son Julian Lennon was at her bedside throughout. The family are thankful for your prayers.
"Please respect their privacy at this difficult time."
Julian also posted a film featuring photographs of his mother, who was 75, and tweeted a picture of her inside a heart with the message In Loving Memory.
Born Cynthia Powell, in Blackpool, she met Lennon at art school in Liverpool in 1957 and the couple married just before Beatlemania transformed her husband from a jobbing musician into one of the most famous men in the world.
At the height of the Beatles' early success, she was kept so far in the background that many of Lennon's female fans were not even aware of her existence, and she stayed at home bringing up Julian while the Fab Four toured the world and topped the charts.
The couple divorced in 1968 after Cynthia discovered her husband's relationship with Japanese artist Yoko Ono.
Hunter Davies, who penned the only official biography of The Beatles in 1968, said Cynthia was "a lovely woman".
He said: "When I was writing the book I spent two years with them, visiting her home and spending time with her.
"She was totally different from John in that she was was quiet and reserved and calm.
"She was not a hippy at all.
"I think it was the attraction of opposites between them. When they got together at art school everyone was amazed - she was seen as refined and reserved and nobody thought they would last.
"John treated her appallingly. He slept with Yoko in their marital home and, as we discovered later, he also physically attacked her but she was loyal to him."
She re-married several times after her divorce and published memoirs of her time with Lennon.
In an interview to publicise one of her books, 2005's John, she told Good Morning America: "I have read so many books and seen so many films, and it's like we don't really exist. We are like walk-on parts in his life. We did spend 10 years together."
Recalling their early days, she said: "You couldn't resist being around him. You couldn't resist watching what he was up to. I mean, he was a total rebel. Everybody was amazed by him".
Lennon's former bandmate Ringo Starr tweeted: "Peace and love to Julian Lennon God bless Cynthia love Ringo and Barbara xx".