Reports at the time also suggested that Diana’s deep unhappiness with her relationship served as her major trigger: “Bulimia nervosa, the eating disorder Diana developed within a year of becoming Princess of Wales, was not (as Charles’s friends have suggested) an illness which made a marriage go sour,” wrote Anthony Holden in a 1993 issue of Vanity Fair. “It was an illness caused by a sour marriage.”

Come 1995, Diana didn’t need an intermediary to fight her battles. In an interview with the BBC,interviewer Martin Bashir asked her about it point-blank: “It was subsequently reported that you suffered [from] bulimia. Is that true?”

“Yes, I did,” she replied. “I had bulimia for a number of years. And that’s like a secret disease. You inflict it upon yourself because your self-esteem is at a low ebb, and you don’t think you’re worthy or valuable. You fill your stomach up four or five times a day—some do it more—and it gives you a feeling of comfort. It’s like having a pair of arms around you, but it’s temporarily, temporary. Then you’re disgusted at the bloatedness of your stomach, and then you bring it all up again.”

When asked if she had told anyone in the royal family about it, Diana said she hadn’t. “You have to know that when you have bulimia you’re very ashamed of yourself and you hate yourself—and people think you’re wasting food—so you don’t discuss it with people,” she explained. “The thing about bulimia is your weight always stays the same, whereas with anorexia you visibly shrink. So you can pretend the whole way through. There’s no proof.”

Her raw, candid confession sent shockwaves through the world at the time—eating disorders were rarely talked about openly. To have a global superstar do so, on such a stage, challenged a major societal stigma.

“For Princess Diana to speak openly about these behaviors and thoughts really shows her strength and her dedication to helping others because it is likely that most people would never have even known she was fighting an eating disorder,” Dr. Kendra Becker, clinical psychologist at Massachusetts General Hospital’s Eating Disorder Clinical and Research Program, tells Vogue of Diana’s legacy. “Her example not only de-stigmatizes eating disorders themselves but also sets an example for seeking help and addressing the shame around these behaviors, thoughts, and feelings that allow them to persist.”

Emma Corrin told Vogue that Diana’s honesty—at the time, an unthinkable act in a family that epitomizes the concept of the stiff upper lip—played a major role in how she approached her portrayal of the late princess. “I was very determined that I didn’t want it just to be alluded to—I didn’t want it just to be a flushing of the toilet or her wiping her mouth,” she said. “I wanted you to see her experiencing it because she was so candid about her struggles with the media, which I think was incredibly ahead of her time.” Corrin and the producers worked closely with Beat, a U.K. nonprofit dedicated to eating-disorder awareness, on the story line to ensure that her scenes accurately captured Diana’s plight without glorifying it. “When it is something that so many people are experiencing,” says Corrin, “it should be properly represented.”