The prince collected the award on Thursday night on her behalf.
Prince Harry was introduced on stage by Ian Walker, and Julian La Bastide, both individuals who experienced meeting the princess in the years of her activist work.
"So in that April, she shook the hand of a 32-year-old man with HIV in front of the cameras", he later said.
Talking to the crowd, Harry said he, and brother Prince William, were incredibly proud of her determination.
"She would be demanding that same access to treatment and testing for young people in Africa and across the world".
"She knew that Aids was one of the things that many wanted to ignore and seemed like a hopeless challenge", he told the awards ceremony in London.
Harry said she understood the disease created a risky situation "when mixed with homophobia".
The Princess made headlines around the world in April 1987 when she opened the UK's first purpose-built HIV/Aids unit that exclusively cared for patients infected with the virus, shaking the hand of a man living with the virus, without wearing gloves, as she did so.
Harry (below) said: 'I believe that she would be telling everyone across society - not just those most at risk - that with effective treatment being free and available in the United Kingdom, that we must all embrace regular testing - both for our own sake and for those that we love.
Attitude unveiled a limited-edition cover with a photo of Diana by Patrick Demarchelier.