Late NFL Star Demaryius Thomas, 33, Had Stage 2 CTE That Led to Cardiac Arrest, Parents Share

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Wide receiver Demaryius Thomas #88 of the Denver Broncos looks on as players warm up on the field before a game at Sports Authority Field at Mile High on November 12, 2017 in Denver, Colorado.
Wide receiver Demaryius Thomas #88 of the Denver Broncos looks on as players warm up on the field before a game at Sports Authority Field at Mile High on November 12, 2017 in Denver, Colorado.

Dustin Bradford/Getty Demaryius Thomas

The parents of Demaryius Thomas, the NFL player who died weeks before his 34th birthday in December 2021, have revealed more information about their son's death in an exclusive interview with ABC News.

The 33-year-old athlete was found unresponsive in his Georgia home on December 9.

Thomas' parents, Bobby and Katina, donated their son's brain to research. Months later, findings reveal that the athlete had suffered Stage 2 CTE and died from cardiac arrest following a separate seizure disorder, according to ABC News.

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Chronic Traumatic Encephalopathy (CTE) is a rare and progressive degenerative brain condition likely caused by repeated head traumas, according to the Mayo Clinic. CTE can only be diagnosed after death, and in a 2017 study of the brains of 111 deceased NFL players, a Boston University researcher found that 110 of them had the disease.

RELATED: What Is CTE? All About Chronic Traumatic Encephalopathy, the Disease Plaguing Former American Football Players

Thomas' parents told ABC News that their son had been struggling with his mental health in the year before his death, including suffering from daily headaches and memory loss.

Demaryius Thomas
Demaryius Thomas

Nick Cammett/Diamond Images via Getty Images Demaryius Thomas

The most common symptoms of CTE include difficulty thinking, depression, memory loss, aggression, impulsive behavior and emotional instability, among others.

According to ABC News, Thomas had opened up to his parents about needing help.

"[Demaryius] would tell me, he was like, 'Mom, I don't know what's goin' on with my body — I gotta get myself together.' And he said, 'I don't feel like myself anymore," said Katina.

RELATED VIDEO: Disease Caused by Concussions and Head Trauma Led to Young Football Player's Suicide: 'He Wanted Us to Tell His Story,' Says Mom

"His mood would change, and he would also isolate himself sometimes," she added.

According to his father, Bobby, Thomas "was paranoid, like, all the time."

RELATED: Peyton Manning Opens Up About Demaryius Thomas' Death: 'It's Been Really Tough'

CTE is a growing concern among athletes, especially within the NFL. When San Francisco 49ers player Jason Hairston died by suicide in 2017, he was suffering from the disorder, which later prompted further research into the condition.

"It is no longer debatable whether or not there is a problem in football—there is a problem," the researcher of the study, Dr. Ann McKee, told the New York Times after Hairston's death.