Read The Powerful Words Prince Harry And Elton John Wrote On This 'ProTEST' Wall

Teaming up for a great cause.

Last week, in what seemed like a normal Facebook Live video, Prince Harry got tested for HIV to end the stigma associated with a disease that afflicts nearly 37 million people.

On Thursday, he continued that same mission by speaking to the International AIDS Conference in South Africa. Three days ago, actress Charlize Theron also addressed the AIDS Conference with a powerful speech about the social side of HIV.

During his speech, the 31-year-old prince recalled the role his mother, Princess Diana, played in fighting AIDS in Africa.

"At the time of the first International AIDS Conference, HIV was a death sentence," Harry said. "Thanks to the work of leaders in the fight against HIV -- people like Nelson Mandela, Sir Elton John, the brave activists of TAG and ACT UP, people like Dr. Peter Piot, and like my mother, Princess Diana -- we have made huge progress."

Singer Elton John also appeared on stage with Harry during the AIDS Conference to answer children's questions.

At the conference, both men teamed up to sign the U.N. AIDS ProTEST wall. It was an empowering display.

"Get tested," Harry wrote on the wall. "Why wouldn't you?"

"Together we can make a change," Sir Elton wrote.

A few days ago, Sir Elton pledged to donate $10 million to support the LGBT community in Africa. The funds will come out of his AIDS Foundation and be used to end stigmas that LGBT people face in Africa.