(CNN) Britain's Prince Harry has thrown his support behind Gareth Thomas, after the Welsh rugby star was forced to go public with his HIV-positive status.

Sharing a picture of the former Wales and British Lions rugby captain on the Sussex Royal Instagram page, the Duke of Sussex commended him for his bravery, saying he was "saving lives" by speaking out.

"Gareth, you are an absolute legend! In sharing your story of being HIV+, you are saving lives and shattering stigma, by showing you can be strong and resilient while living with HIV," he wrote, alongside a picture of 45-year-old Thomas.

"We should all be appalled by the way you were forced to speak your truth, it is yours and yours alone to share on your terms and I and millions stand with you."

On Saturday night, Thomas posted a video on Twitter in which he spoke about his condition for the first time , explaining that blackmailers had threatened to disclose his diagnosis.

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