Former Welsh rugby captain Gareth Thomas shared the powerful story that "changed his perspective on society" on Good Morning Britain on Wednesday morning.
The 45-year-old revealed he was HIV positive in September before completing a gruelling 140-mile Ironman triathlon the following day.
Now the former Rugby star has launched the Tackle HIV campaign with ViiV Healthcare to re-educate people and improve public understanding of HIV to help break the stigma that surrounds it.
Thomas appeared on Wednesday's installment of GMB to discuss his new initiative alongside hosts Piers Morgan and Susanna Reid - as you can see in the video above.
As the interview came to a close Piers Morgan invited his guest to discuss a story from when he was on the tube in London.
"After you made a documentary about you life last year, you were getting off the tube in London," Piers said.
"A guy was walking towards you with headphones on, probably didn't know how loud his voice was and goes, 'I saw your programme about having HIV.'
"You felt, suddenly everyone was looking at you and you didn't know what this guy was going to say and actually he reached out and shook your hand, that must have been a great moment for you?"
Thomas replied: "That was a moment in my life that kind of changed my perspective of society.
"Even though I'd been open and I'd had this huge amount of support I still felt that people were looking at me negatively.
"But that was a moment in my life when I realised people were looking at me because they related to my story.
"Not because they were living with HIV but because everybody has been put into a corner and everybody somehow has to find their way out and people take inspiration from when people tell them how they fought their way out.
"And at that moment with that person I sadly stereotypically thought that he was going to be offensive to me but the reality was he said something to me that changed the way I looked at society."
Good Morning Britain airs weekdays from 6am on ITV1.
