Cynthia Lennon Dead -- John's First Wife Dies from Cancer

John Lennon's first wife Cynthia Lennon ... died at home in Spain after a short battle with cancer. She was 75.

Cynthia and John got married in 1962 .. while she was pregnant -- and she gave birth to Julian Lennon in 1963. He is her only child, and was by her side at her house in Mallorca when she passed away on Wednesday.

Julian posted a pic of his mom with the caption, "You are so beautiful."

John and Cynthia divorced in 1968, but she went on to marry 3 more times.

John was the only Beatle who had tied the knot when they first hit it big. In fact, during their famous "Ed Sullivan Show" debut they put up a graphic saying, "Sorry girls, he's married."