Kelley Mack, the actress who many of us knew as Addy in Season 9 of The Walking Dead, died on August 2, 2025 in Cincinnati. She wasn’t elderly or suddenly ill—her death came after a months‑long battle with a rare and aggressive brain cancer called diffuse midline glioma, which is far from natural causes.
It’s really heartbreaking because she was just 33 and had such a passion for storytelling. Fans also remember her from Chicago Med, 9-1-1, and the indie horror film Delicate Arch. Her sister posted on Instagram that “a bright, fervent light has transitioned,” and shared that butterflies began appearing around loved ones—a symbol they felt reminded them of her.
What Is Diffuse Midline Glioma and Why Is It So Serious?
Diffuse midline glioma (DMG) is a type of central nervous system glioma, which forms deep in the brain—or spinal cord—and is nearly impossible to treat surgically.
- It’s Grade IV, meaning extremely aggressive.
- It most often strikes children or young adults.
- Survival time is sadly low—median survival is around 9–11 months, even with radiation.
Kelley shared that after her diagnosis, she went through an emergency biopsy on her spinal cord which led to loss of mobility in her legs. Surgery was not a cure—just a way to confirm the diagnosis.
How Kelley Discovered Her Illness and What She Experienced
In September 2024, Kelley developed chronic lower back pain. At first, she thought it was a slipped disk. Then a few weeks later her nerve pain started - with itching and shooting pain down her leg. Lying flat became too painful so Kelley spent weeks sleeping upright in a recliner.
Then she had an emergency MRI which showed a mass on her spinal cord, and was diagnosed with diffuse midline glioma. In a groundbreaking Instagram Post she said: because of the biopsy, she lost use of her right leg, and most of her left, and began using a walker or wheelchair.
Despite all of the significant loss, she maintained a positive outlook - in one of her posts, she shared a video of her smiling while walking on stairs, with her partner helping. This type of strength created an aura around her that inspired people regardless of the pain she was enduring.
Kelley had approximately 35 acting credits and 5 producing credits during her career. Kelley studied cinematography at Chapman University and loved telling stories through film or television. Besides Walking Dead, she had guest roles in Chicago Med, 9‑1‑1, and films like Broadcast Signal Intrusion and Delicate Arch. She also did voiceover work, notably match‑voicing Gwen Stacy promos for Spider‑Man: Into the Spider‑Verse.
Her last project, called Universal, was released just months before her passing. She served as executive producer on that too. It’s painful to think she was actively working right up to the end.
Public Tributes & Social Posts
A user @RealKeatonHobby wrote on X:
Such a beautiful young lady we have lost at such a young age. Rest in love, Kelley. 🙏🏻❤️
— Keaton Hobby (@RealKeatonHobby) August 6, 2025
Family Tribute and Upcoming Memorial
Her family posted a touching tribute on Instagram and CaringBridge, sharing that she died peacefully on August 2 with her loving mother and aunt by her side. They described her as a “bright, fervent light” and said butterflies began appearing to them afterward as symbols of her spirit.
A celebration of life service is scheduled for August 16 in Glendal, Ohio, and more remembrances may follow in Los Angeles where she worked for many years.
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