Olivia Munn has revealed she has been privately battling breast cancer.

The "Newsroom" star, 43, shared her diagnosis in an Instagram post on Wednesday, telling fans that she has had four surgeries over the past 10 months and spent "so many days" in bed that she "can't even count."

"Surprisingly, I've only cried twice," she wrote. "I guess I haven't felt like there was time to cry. My focus narrowed and I tabled any emotions that I felt would interfere with my ability to stay clearheaded."

Munn described taking a genetic test in February 2023 in order to be "proactive" about her health, during which she tested negative for 90 different cancer genes. She also said she had a normal mammogram that winter, but she was diagnosed with breast cancer two months later.

Munn shared that she would not have found the cancer for another year, during her next mammogram, if it wasn't for her OB/GYN deciding to calculate her breast cancer risk assessment score. The doctor determined that based on several factors, including Munn's age and family history, her lifetime risk was 37%.

'Violet' star Olivia Munntalks working through 'surround sound of self-doubt,' the best parenting advice

This led Munn to get an MRI, an ultrasound and a biopsy, she said. The biopsy found she had Luminal B cancer, an "aggressive, fast moving cancer," in both breasts, Munn said, adding that she received a double mastectomy a month later.

"I've tended to let people see me when I have energy, when I can get dressed and get out of the house, when I can take my baby boy to the park," Munn wrote. "I've kept the diagnosis and the worry and the recovery and the pain medicine and the paper gowns private. I needed to catch my breath and get through some of the hardest parts before sharing."

Story continues below.

In her post, Munn urged followers to ask their doctors to calculate their breast cancer risk assessment score, reflecting that her OB/GYN's decision to do so "saved my life."

"I'm lucky," Munn also said. "We caught it with enough time that I had options. I want the same for any woman who might have to face this one day."

John Mulaneyconfirms Olivia Munn is pregnant, opens up about rehab

Munn welcomed a son, Malcolm, with comedian John Mulaney in 2021. She thanked Mulaney for "the nights he spent researching what every operation and medication meant and what side effects and recovery I could expect." She also said that Mulaney was always there before and after her surgeries and would place framed photos of Malcolm next to her so it was the first thing she saw when she woke up.

The Instagram post included multiple photos and videos of Munn in hospital beds, including one showing a framed photo of Mulaney and their son on a table.

The actress, who has starred in films like "X-Men: Apocalypse" and "Magic Mike," received a wave of support on social media after sharing her diagnosis.

"Thank you for fighting so hard to be here for us. Malc and I adore you," Mulaney commented.

Niecy Nash, Kaley Cuoco and Monica Lewinsky sent their love in the Instagram comments, with Lewinsky writing, "love you so much smart, kind, beautiful friend. you have been so strong … and know we’re all here to help hold space and continue sending love + light."

Munn's OB/GYN, Dr. Thaïs Aliabadi, also commented on her post, "You are my hero. Your post will save so many lives. I love you so much."