Hosted by Tom Daley, the Attitude Awards recognise the "inspirational stories and outstanding achievements " of key personalities of the LGBT community.
Harry revealed how he and his brother, Prince William are "incredibly proud" of their mother's determination to help change the perception of HIV/AIDS and that progress was being made in the treatment for the diseases.
"In April 1987, my mother was only 25 years old", Harry said in his acceptance speech. She knew that aids was one of the things that many wanted to ignore and this seemed to be a challenge without hope.
Harry said she understood the disease created a risky situation "when mixed with homophobia".
Reflecting on the fearful climate in the '80s, where many believed that the disease could be passed from skin-to-skin contact, the late star's decision to shake hands with a man suffering from the illness was transformative. But in April of 1987, Princess Diana was photographed shaking hands with an old man with HIV.
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"Diana wasn't making that distinction of, 'These people are more important or less important.' It was, 'You are all important.' And she knew that every time she did an announced visit with the cameras there, that would go mainstream". She was using her position as Princess of Wales, the most famous woman in the world, to challenge everyone to educate themselves.
A Kensington Palace spokesman said: "Prince Harry was keen to do this as he has continued his mother's work on HIV/Aids and the awards are in support of the Elton John AIDS Foundation who he has worked closely with".
Last July, the prince got tested for HIV during a Facebook Live demonstration, proving how easy it is to get done. At that time, the prince told the publication, "Then younger generation coming through want to talk about it, but there's still that stigma".
Prince Harry turned up to the Attitude Awards Thursday night to deliver an emotional tribute speech to his mother, Princess Diana, as he collected a Legacy Award on her behalf.
The brothers have spent the last six months commemorating their mother's memory and work leading up to the 20th anniversary of Princess Diana's tragic death in a auto crash in Paris Aug. 31, 1997.