Actress Angelina Jolie has had her ovaries and fallopian tubes removed as a preventative measure against cancer.
Writing in the New York Times, Jolie said she had the surgery last week as she carries a gene that gave her a 50% risk of developing ovarian cancer.
Two years ago, Jolie, whose mother died from cancer, had a double mastectomy.
"It is not easy to make these decisions," she said. "But it is possible to take control and tackle head-on any health issue."
Jolie, who is married to Hollywood actor Brad Pitt, elected to have her ovaries and fallopian tubes removed after a check-up two weeks ago.
In the article, titled Angelina Jolie Pitt: Diary of a Surgery, she said a blood test revealed "a number" of elevated inflammatory markers that could be a sign of early cancer, and was told to see a surgeon immediately.
"I went through what I imagine thousands of other women have felt. I told myself to stay calm, to be strong, and that I had no reason to think I wouldn't live to see my children grow up and to meet my grandchildren," Jolie wrote.
"I called my husband in France, who was on a plane within hours. The beautiful thing about such moments in life is that there is so much clarity. You know what you live for and what matters. It is polarizing, and it is peaceful."
Further tests revealed Jolie was free of a tumour, but elected to have her ovaries removed after consulting doctors. Her mother, grandmother and aunt all died of the disease.
"My doctors indicated I should have preventive surgery about a decade before the earliest onset of cancer in my female relatives," wrote Jolie.
"My mother's ovarian cancer was diagnosed when she was 49. I'm 39."
Writing about the procedure, saying: "It is a less complex surgery than the mastectomy, but its effects are more severe. It puts a woman into forced menopause."
Jolie, who is also a director and UN envoy, will now take hormone replacements.
"Regardless of the hormone replacements I'm taking, I am now in menopause," Jolie said.
"I will not be able to have any more children, and I expect some physical changes. But I feel at ease with whatever will come, not because I am strong but because this is a part of life. It is nothing to be feared."
Charity Ovarian Cancer Action has praised Jolie's decision and "bravery".
"We applaud Angelina Jolie's decision to announce that she has had preventative surgery for ovarian cancer and are anticipating another wave of the 'Angelina Effect', which saw a dramatic increase in the number of women referred for genetic testing after Angelina announced that she had undergone a double mastectomy in 2013," said Katherine Taylor, the charity's acting chief executive.
"While all women in the UK have a one in 54 chance of developing ovarian cancer, for those with a mutation in their BRAC1/2 genes, like Angelina Jolie, the risk increases to one in two.
"If women know they have BRCA gene mutations, they can choose to take action before cancer develops, much like Angelina has. Her bravery to announce this news publicly could save lives."
Jolie, who is married to actor Brad Pitt, has six children, three of whom are adopted.
The Oscar-winning Hollywood star added: "It is not possible to remove all risk, and the fact is I remain prone to cancer. I will look for natural ways to strengthen my immune system. I feel feminine, and grounded in the choices I am making for myself and my family.
"I know my children will never have to say: "Mom died of ovarian cancer."