Olivia Munn is remembering her friend Shannen Doherty.

The Charmed alum passed away on July 13 at age 53 after a yearslong battle with cancer. "The devoted daughter, sister, aunt and friend was surrounded by her loved ones as well as her dog, Bowie," her rep confirmed to NBC News. "The family asks for their privacy at this time so they can grieve in peace.”

After news of Doherty's death emerged July 14, Munn—who shared her breast cancer diagnosis earlier this year—reflected on their bond.

"I am absolutely heartbroken," the Newsroom actress began her Instagram Story tribute. "When I was first diagnosed with breast cancer I remember how she bravely let the world into her journey and reached out to her."

"We became instant friends," Munn continued. "Which I honestly couldn't comprehend at time because watching her on '90210' was everything to me when I was 10."

Munn, 44, noted that they bonded through a shared battle as well as a desire to help other women going through a similar journey.

"Looking back on the last text she sent me just a couple months ago," the X-Men: Apocalypse star added, "she asked how I was doing and if she could do anything for me." 

"True to form, Shannen was offering her support even though she was in the final stage of fighting this horrific disease," Munn, who shares son Malcolm, 2, with husband John Mulaney, added. "Cancer is really f--king scary and Shannen faced it with such dignity, strength and grace."

Munn wrote that she's sending her love to Doherty's mom, Rosa, during this unimaginable time.

She concluded her tribute with a message to her friend, telling her, "Fly so high."

Keep reading to revisit Doherty's cancer journey, in her own words...

Shannen Doherty's health journey began in February 2015, doctors diagnosed her with "invasive breast cancer metastatic to at least one lymph node," according to court documents obtained by E! News.

She underwent a single mastectomy in the same year, before undergoing chemotherapy and radiation treatments.

The Beverly Hills, 90210 alum started experiencing hair loss amid her treatments, leading her to shave her head.

"After my second treatment, my hair was really matted," she told Entertainment Tonight in July 2016. "And I went to try and brush it out, and it just fell out."

It was then Shannen decided to cut her hair, with her mom helping her style it into a "cute little bob."

"But it wasn't enough," she noted, explaining that her hair kept falling out. "I don't know if I'll ever look like me again."

In between rounds of radiation therapy, Shannen underwent reconstructive surgery as a follow-up to her mastectomy  in early 2017. 

In April 2017, the Charmed star announced she was in remission.

"Good news? YES," she wrote on Instagram. "Overwhelming. YES. Now more waiting."

At the time, Shannen noted that "the next five years is crucial" because reoccurrences "happen all the time."

Nearly two years after going into remission, Shannen was informed by her doctors that the breast cancer had returned—this time categorized as stage 4.

She kept the diagnosis within her inner circle until 2020. 

"It's a bitter pill to swallow in a lot of ways," she told ABC News. "I definitely have days where I say, ‘Why me?' And then I go, ‘Well why not me? Who else? Who else beside me deserves this?' None of us do."

Despite the disheartening diagnosis, Shannen insists she's "not signing off."

"I feel like I'm a very, very healthy human being," she said in the October 2020 issue of Elle. "I'm not ready for pasture. I've got a lot of life in me."

By 2023, the cancer had metastasized to Shannen's brain and spread to her bones.

"I don't want to die," she told People. "I'm not done with living. I'm not done with loving. I'm not done with creating. I'm not done with hopefully changing things for the better. I'm just not—I'm not done."

Shannen underwent surgery to have a tumor removed from her brain in January 2023.

“We got almost all," Shannen shared on her Let's Be Clear podcast, "and the rest we handled with brain radiation.”

However, she also experienced major setbacks in her road to recovery, including a "horrible reaction with steroids" she was taking at the time.

"I tried to cut it down, and then the brain would swell a little bit more, and the hand would stop working completely," she told People, explaining that she lost the ability to hold an object in her right hand for three months. "The first time a glass slipped right through my hand, I was like, 'No, no, no, no, no. This is not happening.'"

In April 2023, Shannen filed for divorce from her husband of 11 years Kurt Iswarienko, listing the separation date as Jan. 15, 2023 in documents obtained by E! News.

The BH90210 actress later accused Kurt of cheating on her during cancer treatments, saying that she learned of his alleged two-year affair moments before undergoing brain surgery.

"I went into that surgery early in the morning and I went in after I found out that my marriage was essentially over," Shannen shared in a December 2023 episode of Let's Be Clear. "I couldn't go into that surgery with him there. I felt so betrayed."

Kurt has not publicly addressed the allegations. E! News reached out to his rep for comment but didn’t hear back.

Shannen shared in January 2024 a new infusion treatment plan she was put on yielded positive results.

"After the sixth, seventh treatment we really saw it breaking down the blood brain barrier," she said on her podcast. "Do I call that a miracle? For me, that happens to be a miracle right now."

In preparation for another round of chemotherapy, Shannen shared that the procedures left her "exhausted."

"It becomes very real in an incredibly different way," she said of her cancer journey on a June 2024 episode of her podcast, "because I have no idea how long I'm gonna be on the chemo for."