Former Wales captain Gareth Thomas has revealed he has been living with HIV "for years" and appealed for support to "break the stigma" around the condition.
Thomas, 45, said in a video posted on Twitter that he had been moved to go public about his health because he had received emails threatening to expose him.
"I'm Gareth Thomas and I want to share my secret with you. Why? Because it's mine to tell you, not the emails that make my life hell, threatening to tell you before I do, and because I believe in you and I trust you," he said.
"I'm living with HIV. Now you have that information, that makes me extremely vulnerable but it does not make me weak.
"Now even though I've been forced to tell you this, I choose to fight, to educate and break the stigma around this subject."
Thomas was capped 100 times for Wales in an international career spanning 1995-2007 and also captained the British & Irish Lions in 2005.
After his retirement from international rugby, he came out as gay in 2009 and has been a prominent campaigner against homophobia in sport. In an interview with the Daily Mirror, Thomas said he had kept the diagnosis secret for years and it initially caused him to have suicidal thoughts.
"I had a fear people would judge me and treat me like a leper because of a lack of knowledge," the paper quoted him as saying. "I was in a dark place, feeling suicidal. I thought about driving off a cliff.
"To me, wanting to die was just a natural thought and felt like the easier way out, but you have to confront things. And having a strong support system and the personal strength and experience of overcoming those emotions got me through it."
The first British rugby international to come out, Thomas told the paper that blackmailers had threatened to reveal his diagnosis. He also said he was in good health while managing the condition with medication, and Stephen, his partner of several years, was not HIV positive.
Thomas' revelation comes just over a week before Wales play their first World Cup match against Georgia in Japan, where the former skipper will work as a pundit for British broadcaster ITV.
"I'm asking you to help me to show that everyone lives in fear of people's reactions and opinions of something about them. But that doesn't mean that we should have to hide," he said on Twitter.
"To do this, I really, really need your support."
The post prompted a flood of supportive messages from British sport personalities on social media, including former England football great Gary Lineker and prominent international rugby referee Nigel Owens. Welshman Owens, who came out as gay in 2007 after a long struggle to come to terms with his sexuality, gave "all (his) support" to Thomas on Twitter.