Tragic Loss: '9-1-1' Star Kelley Mack Dies at 33 After Courageous Glioma Fight

Kelley Mack, known for her roles in 9-1-1 and The Walking Dead, has tragically passed away at the age of 33.

Her sister, Kathryn, broke the heartbreaking news through Kelley's Instagram account on Tuesday, August 5. "It is with indelible sadness that we are announcing the passing of our dear Kelley," she wrote. "Such a bright, fervent light has transitioned to the beyond, where we all eventually must go."

The message revealed that Kelley "passed peacefully" on Saturday, August 2, surrounded by her loved ones, including her mother, Kristen and aunt, Karen.

"Kelley has already come to many of her loved ones in the form of various butterflies 🦋 ❤️," the post continued. "She will be missed by so many to depths that words cannot express."

Katherine emphasized her sister's appreciation for her supporters: "She would want you all to know how much she loves you," the heartfelt message stated. "And as her sister, I want you all to know how brave that tough SOB was, especially when she decided to make the leap to be reunited with God. I'm so f----- proud of her."

Kelley, born Kelley Lynne Klebenow, began her acting journey in commercials at a young age and later earned an Acting Award from the Tisch School of the Arts for her role in The Elephant Garden (2008).

Mack gained significant recognition for her role as Addy in five episodes of The Walking Dead (2018-2019). Her guest appearances in popular shows like 9-1-1 and Chicago Med were also well-received. Beyond live-action, she lent her voice to Gwen Stacy in the Oscar-winning animated film Spider-Man: Into the Spider-Verse. Mack was also a producer, writer, director and editor, with notable short films like A Knock at the Door.

According to Kelley's online obituary, the actress lost her battle with glioma, a type of tumor that originates in the brain or spinal cord. The Mayo Clinic defines glioma as a growth of cells that begins in the central nervous system.

Kelley shared her diagnosis of diffused midline glioma in January, after getting checked for lower back pains, and "shooting" pains in her legs.

"I have been diagnosed with #diffusemidlineglioma, an extremely rare type of #astrocytoma #cancer. Due to the biopsy surgery on my spinal cord, I have lost the use of my right leg and most of my left leg, so I now get around with a walker and a wheelchair," she said on Instagram, adding that she had to sleep in a recliner for a month.

By March, Kelley finished proton radiation treatments, while revealing she'd been undergoing physical therapy.

A celebration of life honoring Kelley has been scheduled for Saturday, August 16, in Ohio, with a remembrance event in Los Angeles to follow at a later date.