His girlfriend early in his career, Diana Hyland, also died of breast cancer. He met her when they both filmed "The Boy in the Plastic Bubble" in the mid-70s and their relationship quickly became romantic about a month in. I think she played his Mom in the film. She died at 41. John has plenty of experience dealing with death and those close to him who died from breast cancer...more than one man ever should.
God she was so good looking but from what I have read, a really good person. I watched some of her old videos last week such as Make a Move on Me and A Little Love. She was so hot in those videos- she was one of those people who was not capable of looking bad. Sheena Easton was another singer like that.