In a new documentary, Diana Our Mother: Her Life and Legacy, which commemorates the 20th anniversary of her death, Elton John sits down with Prince Harry at the London Lighthouse Aids Centre to remember the late Princess' dedication to AIDS activism.

“[AIDS] was considered to be a gay disease," Sir Elton said, punctuating how Diana helped eradicate widespread stigma. “And for someone who was within the Royal Family, and who was a woman, and who was straight—to have someone care from the other side was an incredible gift."

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In the clip, Sir Elton and Prince Harry are shown looking through photos of Diana visiting the AIDS foundation, where she personally shook hands with patients. “I haven't experienced many people in my life who have that ability, but she could walk into a room of people and make them feel that everything was great," Sir Elton said.

Watch, below, ahead of the doc's HBO premiere on Monday, August 31.