American actress Kelley Mack best known for her role as Addy in AMC’s The Walking Dead, has passed away at 33.

She passed away in her hometown of Cincinnati, Ohio, last week, her family confirmed in an online statement on Tuesday. The cause of death was an aggressive tumor that attacked her central nervous system.

Her family described her as a bright, fervent light and said she would be deeply missed. They also shared that many loved ones had felt her presence symbolically through butterflies.

In January, Mack shared her recent diagnosis on Instagram, where she revealed she was diagnosed with a rare type of astrocytoma cancer. It is a cancerous tumor that develops in the central nervous system, beginning in the brain or spinal cord. 

Kelley disclosed that she had initially experienced persistent lower back pain, believing it was a slipped disc. “Then, shooting pains in my legs and back began, which forced me to sleep in a recliner for a month because lying down was too painful,” she wrote on Instagram.

An emergency MRI scan later detected an abnormal mass in her spinal cord. Following biopsy surgery, Mack lost most of her ability to move her legs and began using a wheelchair and walker. “It has been a very emotional and challenging time, truly testing my mental fortitude, faith, and physical strength,” she wrote.

She received radiation treatment in Cincinnati and remained hopeful throughout. In March, she shared a video of herself walking up a set of stairs, calling it “a big deal for me.” She also posted updates on Universal, an independent film in which she starred.

This condition, also known as diffuse midline glioma, is more commonly found in children but can occur in adults as well, according to the Brain Tumor Center at the University of California, San Francisco. 

The National Cancer Institute noted that the exact cause of abnormal astrocyte growth remains unknown.

She was born Kelley Lynne Klebenow on July 10, 1992, in Cincinnati. 

She completed her studies at the Dodge College of Film and Media Arts at Chapman University in 2014. Her parents, Kristen and Lindsay Klebenow, along with her siblings Kathryn and Parker, survive her. 

Mack earned 35 acting credits during her career, including her breakout role as Addy in The Walking Dead (Season 9). She also appeared in NBC’s Chicago Med, Fox’s 9-1-1, and various independent projects.