Princess Diana and Prince Charles
Princess Diana used charities as a secret weapon against the royal family. Pictured: Prince Charles and Princess Diana at Westminster Abbey, London, for a centenary service for the Royal College Of Music on Feb. 28, 1982. Getty Images/Fox Photos

Princess Diana had supported hundreds of charities when she was still alive.

Prince William and Prince Harry's mom was very active when it comes to charities. In fact, due to her dedication in helping the people, she was dubbed as the People's Princess. However, according to Netflix's "The Royal House of Windsor" documentary, this is Princess Diana's secret weapon against the royal family.

"Charity has always been a secret weapon of the monarchy but the charity the Queen supported were uncontroversial charities," the narrator read (as quoted by Express). "Diana saw the possibility of getting much more publicity by dealing with Leprosy, by dealing with aids victims."

Among Princess Diana's most popular works were changing the public's perspective and attitudes on AIDS. In 1987, she opened an HIV/AIDS unit in London's Middlesex Hospital and even shook hands with a patient to show the world that the disease is not communicable by simply shaking hands.

However, as Princess Diana won the heart of the public, the same charities made her relationship with the senior royals challenging. In fact, the Queen reportedly intervened and asked her to get involved with something "nicer and more pleasant" rather than the controversial charities she chose.

The royals compared Princess Diana's compassion to that of King Edward VIII who once kissed a disfigured soldier in the First World War. So, they urged her to support other charities that they thought would make her happier.

Prince Harry has carried on her mom's charities. In fact, the Duke of Sussex made a trip to Lesotho in southern Africa in June without his wife, Meghan Markle.

Prince Harry trip was deemed as a "private visit." He unveiled a plaque at the new community hall, donated by his charity, Sentable, to mark its official opening. He co-founded the charity with Prince Seeiso of Lesotho in 2006.

The charity's name means "forget me not," a bid to improve the thousands of children and young people affected by HIV/AIDS in the country.

In related news, Prince Charles wrote a letter suggesting that he doubted his proposal to Princess Diana. The never-before-read letter was unearthed on Netflix's "The Royal House of Windsor" documentary.

"I’m terrified sometimes of making a promise and then perhaps living to regret it," Prince Charles wrote.