Former NBA player Jason Collins, 47, reveals heartbreaking first symptom before being diagnosed with aggressive brain cancer

Former NBA player Jason Collins has confirmed a heartbreaking cancer diagnosis after a rapid and sudden onset of symptoms.

Collins, 47, detailed in ESPN on Thursday that doctors had found 'one of the deadliest forms of brain cancer' earlier this year, and confirmed that he had been diagnosed with a Stage 4 glioblastoma.

The former basketball player, who came out as gay in 2013 and became the first NBA player to do so publicly, had hinted at the devastating health diagnosis in a brief and vague statement released in September, which was released by his family as he was 'mentally unable to speak for myself.'

He also detailed how his initial cancer symptoms 'came on incredibly fast', with an early warning sign coming in August as he prepared to head to the US Open with husband Brunson Green.

Despite the much-anticipated trip with the 'love of his life', when a cab came to take them to the airport, Collins was 'nowhere near ready'. Perplexingly, the couple would ultimately miss their flight as the athlete was unable to concentrate on packing.

Jason Collins (right) came out in 2013 and became the first openly gay NBA player when he signed for the Nets a year later (Justin Edmonds/Getty Images)

This gave the couple pause for thought, but Collins' sportsman's mindset told him to carry on.

He explained: "I had been having weird symptoms like this for a week or two, but unless something is really wrong, I'm going to push through. I'm an athlete."

But these brain fog symptoms would continue, forcing Collins to seek out specialist care.

The former Brooklyn Nets player said he was in a CT machine 'for all of five minutes' before it became clear that something was wrong.

What happened in the following hours would have been truly terrifying. Collins said: "In hours, my mental clarity, short-term memory and comprehension disappeared -- turning into an NBA player's version of Dory from Finding Nemo."

Doctors would find a dangerous glioblastoma growing in his brain, buried deep and pressing on his frontal lobe, which controls a large number of essential functions, from problem-solving to attention span.

Sadly for Collins, this cancerous growth had already spread into both hemispheres of his brain.

He explained: "My glioblastoma is 'multiforme.' Imagine a monster with tentacles spreading across the underside of my brain the width of a baseball."

Collins has said he wants to share his fatal diagnosis for the same reason he told the world he is gay (ROBYN BECK/AFP via Getty Images)

Collins, with the support of his loved ones, was encouraged to fight the tumor and has flown around the world to receive cutting-edge treatments in the hopes of delaying the spread of the hard-to-treat growth.

However, even with targeted radiotherapy and chemotherapy alongside other new cancer medications, the NBA star said the average life expectancy for someone in his condition is just 11 to 14 months.

In his own touching words, the history-making sportsman shared why telling his story with such honesty was so important, with just weeks or months to live.

Collins wrote: "One thing I've always prided myself on is having the right people in my life. When I came out publicly as the first active gay basketball player in 2013, I told a lot of the people closest to me before I did so.

"I wasn't worried it would leak before the story came out, because I trusted the people I told. And guess what? Nothing leaked. I got to tell my own story, the way I wanted to.

"And now I can honestly say, the past 12 years since have been the best of my life. Your life is so much better when you just show up as your true self, unafraid to be your true self, in public or private."

If you’ve been affected by any of these issues and want to speak to someone in confidence, contact the American Cancer Society on 1-800-227-2345 or via their live chat feature, available 24/7 every day of the year.