Renee Tuck's brother Shane had been retired from football only a few years when he told her he was hearing voices, "and they weren't very nice."
The courageous midfielder, who'd spent almost a decade playing in the elite Australian Football League, was a loving family man, music lover, and had never experienced anxiety.
"Shane wasn't a mentally unwell guy, he was a go-getter," she told 7.30.
"He didn't suffer anxiety and depression and he loved life, he lived it to the full, [just like] how he played his football.
"When he said there were some things going on, I was very concerned because I knew him well enough to know this is not him."
Shane Tuck quickly deteriorated.
His family say he became "withdrawn and confused" as his brain became consumed by those voices in his head.
"While we thought he might not be listening, he was so traumatised by what was going on in his mind," she said.
"So while we thought he was distant, he was just fighting every moment to stay alive."
After multiple visits to specialists, and even a bout of electro-shock therapy, Shane's condition failed to improve.
Renee says her brother's final months were "completely and utterly traumatising and soul destroying".
"All of a sudden he's slowly leaving, you could see in his eyes he was slowly leaving," she said.
Shane died in 2020 at just 38.
Immediately after his passing, the family donated his brain to Michael Buckland, a renowned neuropathologist and the founder of the Brain Bank.
Dr Buckland had been researching a disease known as chronic traumatic encephalopathy (CTE), which can only be diagnosed post-mortem, by examining the build-up of a brain protein known as tau.
"Shane's brain was the worst I'd ever seen in terms of pure CTE, and that came as a real shock," Dr Buckland said.
"In fact, when the scientist handed me the microscope to look [at the brain], I didn't even need the microscope to see the accumulation of tau.
"He was a young man, and to see that level of disease was quite shocking."
When the Tuck family received the diagnosis, everything started to make sense.
"He wasn't mentally unwell, and it was a diseased brain that had been dying on him," Renee said.
"It just helped us unbelievably so, because it just made so much sense and that's been very helpful in our healing and moving forward."
Shane's death is now the subject of a coronial inquest.
The findings are expected to be handed down once the AFL provides the court with details of its own investigation into concussions and the league's relationship with controversial neurologist Paul McCrory.
But Renee says her family's main focus is to now raise awareness of CTE and promote more research so families can better understand what sufferers are going through.
"It's a club that no one wants to be a part of, but it is one that exists, and if you need support you absolutely [should] reach out," she said.
"I'm working with some families now that have lost their loved ones but I think awareness in prevention is where this is going to start, because It's real and it's not going anywhere and it's highly traumatic."
Recently, the brain of former rugby league player and coach Paul Green was donated to Dr Buckland, and he is hoping to secure more brain donations to better understand the disease.
Watch this story on 7.30 tonight on ABC TV and ABC iview.
