Prince Harry and Sir Elton John have joined forces to launch a global organisation aimed at targeting HIV infections in men.
The Duke of Sussex, 33, said he was "honoured" to share the stage with Sir Elton at the International AIDS Conference in Amsterdam to launch the MenStar Coalition.
The initiative is aimed at targeting and preventing HIV infections in men.
Harry attended the event in his role as co-founder of the Africa-based charity Sentebale, which helps young people living with HIV.
"I am honoured to be sharing the stage with someone who has always put people at the centre of his work," Prince Harry said.
"For over a quarter of a century he has worked tirelessly to fund research services and communities around the world."
"Today, he has come to Amsterdam to announce his latest endeavour: a billion dollar global partnership to break the cycle of male transition of HIV - particularly in sub-Saharan Africa," he continued.
The initiative was sparked by the "growing alarm of the rate of new HIV infections among young women," the Duke of Sussex said, adding that the root of the problem was "the lack of awareness of HIV prevention amongst hard-to-reach young men."
“We succeed when we put people at the heart of our strategies – when we harness the huge potential of people living with HIV to help guide the delivery of services; when we create platforms for young people to shape and direct the services they rely on.” – The Duke at #AIDS2018 pic.twitter.com/1UpkR6XG8h— Kensington Palace (@KensingtonRoyal) July 24, 2018
Sir Elton also addressed the issue of men failing to get tested for HIV - and said the MenStar Coalition was aimed at teaching men to protect themselves.
He warned that 24-35-year-old men were getting tested and treated for HIV at "unacceptably low rates".
"Young people are the only age group where HIV infections are rising, not falling," said the pop star and veteran AIDS campaigner.
"We have to do much, much more to bring men, especially younger men more fully into the fold."
The coalition brings together different partners - including the UN's Unitaid and the US fund PEPFAR.
The new initiative focuses on "the tough but essential work of truly changing mindsets," Prince Harry added.
Speaking during Monday's discussion session, Harry told young advocates from Sentebale: "More and more leaders, they should be using the younger generation and the experiences you have - I'm 33 years old and I already feel out of touch.
"We have to put power into the hands of the younger generation.
"Because that's where the solutions are going to come from, that's where the passion and engagement is coming from as well."
The royal has followed in the footsteps of his mother Diana, Princess of Wales in the fight against AIDS in recent years - raising awareness about HIV/AIDS and encouraging people to get tested.
Sir Elton recently performed at Harry and Meghan's wedding.