Diana worked to help those with HIV/Aids and Harry, 28, is doing the same in the tiny kingdom of Lesotho that he has been visiting this week.
The Prince spoke after a whirlwind visit to the kingdom. There, he checked up on the work of the charity Sentebale that he set up with friend Prince Seeiso in memory of their late mothers.
Addressing a gala dinner in Johannesburg in neighboring South Africa, Harry said he hoped both mothers would be looking down with pride. "I hope she would be proud of what we are trying to achieve in her name," he said of Queen Mamohato Bereng Seeiso. "I hope that my mother will be proud, too."
Maybe, just maybe, they are together somewhere up there, with blueprints and sketches already mapped out! I can only hope we put the swings in the right place," he told the guests.
"Talking about HIV and understanding it isn't dangerous," Harry said at the dinner. "Denying it, or not knowing about it, definitely is."
And he sensed their efforts were beginning to have an effect. "We are now seeing many of these children begin to fulfill their ambitions and realize dreams that once seemed completely impossible."
Harry added, "Our aim and hope is that we can influence a decline in the transmission of HIV and increase life expectancy, in a unique way for Lesotho: by addressing the psychological and social needs of the next generation, which is so important.
"The future of this very small and beautiful country, and its magnificent people, could and should be very bright."