London (CNN)Former Welsh rugby star Gareth Thomas has revealed he is HIV positive and has vowed to help "break the stigma" surrounding the illness.
Thomas is believed to be the first British sportsman to announce that he is living with the virus. He was also the first professional rugby union player to announce that he was gay, when he came out in 2009.
The former British Lions captain, 45, said he was forced to announce his condition after being threatened with blackmail.
"Hello I'm Gareth Thomas, and I want to share my secret with you," he said in a video posted on his Twitter page. "Why? because it's mine to tell you, not the evils who have made my life hell, threatening to tell you before I do, and because I believe in you and I trust you.
"I am living with HIV; now you have that information that makes me extremely vulnerable, but it does not make me weak."
He added that while he is being "forced" to announce his condition, he pledged to "fight to educate and break the stigma" surrounding the illness.
"I am asking you to help me to show that everyone lives in fear of people's reactions and opinions... But that doesn't mean we should have to hide, but to do this, I really, really need your support," he said.
Thomas said in an interview with the Sunday Mirror that he had been living with "this secret for years," and that the "shame" he felt from his diagnosis left him feeling suicidal.