She died "following a short but brave battle with cancer," reads a statement on Julian Lennon's official website, which features a video tribute to the mother of the artist and musician.
Can't see the video? Watch it here
"Her son Julian Lennon was at her bedside throughout," says the statement. "The family are thankful for your prayers. Please respect their privacy at this difficult time."
Cynthia Powell was born in the British seaside town of Blackpool, Lancashire, in 1939.
She was 18 years old when she met burgeoning rock star and fellow Liverpool College of Art student John Lennon. The pair wed in 1962 after it was learned she was pregnant.
But the couple kept their relationship under wraps for a time as the Beatles were gaining popularity, heading into the thralls of Beatlemania, which hit a crescendo when the group made its North American debut in 1964.
Life in the public eye
Julian Lennon was born in 1963, as the Beatles were causing a stir in the U.K. with the release of their hit singles Please Please Me and She Loves You.- CBC DIGITAL ARCHIVES | 1964: The Beatles conquer North America
- QUIZ | YEAH, YEAH, YEAH! Test your knowledge of the Beatles' British invasion
The Lennons divorced in 1968, after the Beatles guitarist and singer started a controversial relationship with Japanese artist Yoko Ono.
Cynthia Lennon shared stories about their troubled marriage in two books:- The 1970 memoir A Twist of Lennon,
- The 2005 biography John.
"He was a very jealous young man at the time, and he had a lot of pain inside," Cynthia Lennon said in 2005. "He wanted to trust me and he thought by seeing me dancing with a friend of his that I was being disloyal or messing around. So he smacked me, but that was the only time."
John Lennon was assassinated in 1980 outside the Dakota building where he lived with Ono and their son, Sean.