A little known fact about Yoko Ono is mentioned in this biography:
After the collapse of her relationship with Ichiyanagi she married the American producer and art promoter Anthony Cox, and they had a daughter, Kyoko.
. . .
In 1966 Ono held a show at the Indica Gallery, London. John Dunbarwas the gallery’s director. “I introduced John and Yoko,” he recalls. “I was a friend of John and Paul, and suggested they come in; I thought John would enjoy it. Yoko had never heard of John. I had to explain that he was a rich person who might buy something … It wasn’t immediately clear that anything was going to happen. She is a strong woman. John had never met anyone like her.”
After two years they got together. But the corollary was that Cox, after a custody battle for Kyoko that Ono won, effectively kidnapped the child, and Ono did not see her at all between the ages of eight and 31.
Children's Rights Council of Japan (Japan child abduction) 