Lady Diana was a great woman who wanted to create public awareness for HIV and AIDS patients. She worked hard to change people's perspective on "breaking the false stigma of casual contact." For instance, hugging or touching someone that was infected doesn't mean you will get infected, therefore, you should not be treating them any different.
Prince Harry wanted to highlight one of his mother's most famous image with an AIDS patient. 'When she shook hands with a 32-year-old man who had HIV in front of all the cameras, she knew exactly what she was doing, used her position as Princess of Wales, the most famous woman in the world, to challenge the whole to educate themselves, to have compassion, and to reach out to those who need help rather than set them apart'. Prince Harry wanted to make it clear that both him and his brother are still very proud of their mother for her self-less actions.