Mario Fenech's battle with chronic traumatic encephalopathy [CTE], a type of dementia caused by repeated head knocks, caused the South Sydney great to forget his son's wedding.
A gutsy State of Origin representative, Fenech's name became synonymous with the Rabbitohs across a professional career that spanned 15 seasons in the 1980s and '90s.
But at age 53, Fenech was diagnosed with CTE, which has had increasingly devastating effects on his life in the seven years since.
"When I was playing football, I got smashed around the head all the time and it had a real bad effect on me," Fenech told Channel 7's Spotlight.
"You feel like you're going pop and it affects your brain.
"There are times I get really bad, just anxiety stuff."
Fenech's neurologist Dr Rowena Mobbs explained the rugby league great's brain was akin to that of an 80-year-old patient as a result of CTE.
"Gradually the neurons wither away in the brain. There's a loss of brain tissue," she said.
"It won't be long before he needs care."
The condition has begun to have a serious impact on Fenech's family life.
Fenech's son Joe told Spotlight his father gave a speech at his wedding, only to forget that he had done so a day later.
"My parents woke up in the morning, the day after the wedding, my dad turned to my mum and said, 'I'm really excited for the wedding, when is it?'," he said.
Fenech's wife Rebecca said the effects of Mario's condition were felt daily.
"Every day he wakes up now and says, 'I'm confused. I don't know why. I don't feel great'," she said.
"He can't really do or think for himself."
The Fenech family's revelations come as the first full NRL season with an independent doctor in the bunker approaches its conclusion.
But Fenech said he had no regrets playing rugby league in a time when concussion management was far less stringent.
"Rugby league in this generation is a lot safer than when I played," he said.
"But in saying that, I wouldn't change a thing.
"I really enjoyed my 15-year challenge of playing rugby league and enjoyed my time at Souths and it was brutal in those days but that's the way it was."