The actor Ryan O’Neal is to marry Farrah Fawcett, who is dying of rectal cancer.

The star of Love Story told ABC News that his long-time partner had agreed to marry him as she fights the losing battle. The actress, best known for her role in Charlie’s Angels, has abandoned treatment for the cancer which has spread through her body.

O’Neal, 68, said in an interview to be aired later this week: “I’ve asked her to marry me, again, and she’s agreed.” Asked to describe Fawcett’s current health condition, he replied: “She’s fighting for her life.”

The couple have been romantically involved off-and-on since 1982. They have a 24-year-old son, Redmond, together but have never married.

“I used to ask her to marry me all the time,” O’Neal said in an interview with Barbara Walters for ABC’s 20/20. “But it just got to be a joke, you know.”

O’Neal has been a constant presence at Fawcett’s side since news of her illness broke. Last month he told People magazine that the cancer had spread to her liver and that her treatment had effectively ended. He said her trademark blonde hair had dropped out.

“It’s a love story. I just don’t know how to play this one. I won’t know this world without her,” he said. “Cancer is an insidious enemy.”

Fawcett, 62, had rectal cancer diagnosed three years ago and had surgery to remove a tumour but the cancer returned.

Millions watched a documentary about her fight last month. Their son, who is currently in jail on drug charges, was allowed out to see her.

Last month the actress told The Los Angeles Times that she did not like having to fight her battle with cancer in public. “People call, ‘How are you?’ ‘How do you feel?’ ‘We’re praying for you.’ ‘Do you still have your hair?’ ‘What do you feel like?’ When every single call is that kind of call . . . It’s all you talk about, it’s all-consuming. Then your quality of life is never the same.

“I’m holding on to the hope that there is some reason that I got cancer and there is something — that may not be very clear to me right now — that I will do.”

Explore Celebrity

• People

Times recommends

• How to solve the big style questions
• Aids in Africa: ‘It is the staff who really inspire you’
• Video: How to do Beyonce's 'Single Ladies' dance