Sir Elton John has launched an ambitious global project to encourage men to test themselves in the fight against the Aids epidemic.
The singer said more work is needed to bring young men "into the fold" as a solution to end the scourge of the HIV virus, which is growing among certain groups.
The Duke of Sussex introduced Sir Elton as he launched the billion-dollar MenStar Coalition at an international Aids conference in Amsterdam, and praised the star for campaigning to eradicate the disease.
Sir Elton, who performed at Harry's recent wedding reception, told the delegates: "If we want to end Aids once and for all, we must make men part of the solution.
"It is time there was a global coalition to teach men to protect themselves, and in doing so it will teach them to better protect not only their wives and girlfriends, their sisters and daughters, but also critically their brothers and sons."
The project will begin in Africa next year, where men across the continent will be encouraged to self-test for HIV, in a bid to empower them to seek treatment if positive and help stop the spread of the virus.
Sir Elton said recent research had shown that men aged 24-35 were tested and treated for the HIV virus at "unacceptably low" rates.
He added: "We must find ways to change this. Too often, and for good reason, men have been seen as the problem in the fight against Aids.
"So in response we have done so much to safeguard women and girls, and rightly so, but we can't solve the whole problem if we're only addressing half the situation.
"If we want to end Aids once and for all, we must make men part of the solution."
The MenStar Coalition partners, which have raised a billion dollars in initial funding, feature a number of organisations including the Elton John Aids Foundation, the US President's Emergency Plan for Aids Relief (Pepfar) and Unitaid.
In his introduction, Harry said: "For over a quarter (of a) century, Elton has worked tirelessly to fund research and services in communities around the world.
"And today he has come to Amsterdam to announce his latest endeavour - a billion dollar global partnership to break the cycle of male transmission of HIV, particularly in sub-Saharan Africa."