Kelley Mack's Cause of Death: How Did 'The Walking Dead' Star Die?

Kelley Mack, the actress who played Addy on The Walking Dead, has died at 33.

The news came as a shock to many fans, even though Mack had previously shared her health struggles.

According to The New York Times, her cause of death was “an aggressive tumor that attacked her central nervous system,” as confirmed by her family.

She died in Cincinnati, Ohio, over the weekend, with her family announcing the news on August 5.

Back in January, Mack had revealed she’d been diagnosed with an astrocytoma—"a kind of cancerous tumor that grows in the central nervous system, beginning in the brain or the spinal cord. It is also known as diffuse midline glioma," The Times reported.

According to the Mayo Clinic, astrocytoma is a type of tumor that forms in the brain or spinal cord, originating in star-shaped cells called astrocytes, which help support and connect nerve cells. The exact cause is often unknown.

A statement on Mack's Instagram page announced her death.

"It is with indelible sadness that we are announcing the passing of our dear Kelley. Such a bright, fervent light has transitioned to the beyond, where we all eventually must go," the post says.

"Kelley passed peacefully on Saturday evening with her loving mother Kristen and steadfast aunt Karen present. Kelley has already come to many of her loved ones in the form of various butterflies 🦋 ❤️. She will be missed by so many to depths that words cannot express."

It didn’t take long for reactions to pour into the comments section.

Cast and crew members from The Walking Dead shared emotional tributes to Mack, remembering her warmth, talent, and impact both on and off set.

“What an incredible human. So proud to have fought alongside her in our final episode together,” wrote actress Alanna Masterson. Gustavo Gomez added, “This is heartbreaking. I feel so lucky that our paths crossed. Your bright light will always shine on.” Director Michael E. Satrazemis also paid tribute, calling Mack “a bright light on every level” and sending love to “those who love her.”