08/22/2017 11:41 EDT | Updated 08/22/2017 13:26 EDT

Prince William Says He's Proud Of Princess Diana For Opening Up About Her Bulimia

Diana first revealed she had an eating disorder in 1992.

PA Wire/PA Images

It can be difficult to tell your family that you're battling a mental health disorder — even more so when you're a member of the Royal Family and you're letting the world know that you aren't as "perfect" as they assume you to be.

But that's exactly what the late Princess Diana did, when she first revealed she had suffered from bulimia in Andrew Morton's book Diana: Her True Story in 1992, and opened up about her eating disorder again in an interview with Panorama in 1995.

Diana, Princess of Wales, arrives at the Lille Congress Hall on November 15, 1992 for the opening of Paul McCartney's oratorio 'Liverpool'. / AFP PHOTO / AFP PHOTO AND POOL / Jacques DEMARTHON (Photo credit should read JACQUES DEMARTHON/AFP/Getty Images)

It's Diana's bravery for being willing to be vulnerable and speak out about her disorder, which is considered a mental illness, that makes her son, Prince William, proud.

During an interview for a new documentary focused on eating disorders, the father-of-two opened up about his late mum's battle with bulimia, Hello! reports. William chatted with former ITN newsreader Mark Austin and his daughter Maddy, who was diagnosed with anorexia in 2012, but has since made a full recovery.

The fact you are speaking out is incredibly brave, but it should become very normal.

During their talk, Will said that there's a need to "normalize the conversation around mental health," adding, "The fact you are speaking out is incredibly brave, but it should become very normal."

Maddy touched upon the fact that Diana spoke openly about her bulimia, saying, "I was really inspired by what your mum did," to which the Duke of Cambridge replied, "We need to be matter-of-fact about it, and not hide it in the dark where it festers."

Dylan Martinez / Reuters
The Prince of Wales, Prince William, Princess Diana and Prince Harry attend the Heads of State ceremony in Hyde Park in London May 7, 1995.

Austin also asked the prince whether he's proud of Diana for sharing her experience with the world.

"Absolutely," William replied. "These things are illnesses and they need to be treated. Mental health needs to be taken as seriously as physical health."

Mental health needs to be taken as seriously as physical health.

Later in the interview he added, "I really hope George and Charlottecan grow up in a world where mental health is completely normalized and where we can all talk about it openly and honestly. We can talk about stuff and it is not a weakness and not to be ashamed of."

Talking about mental health has been an important issue for Prince William for a few years now.

Recently, the 35-year-old FaceTimed with Lady Gaga for a frank discussion about mental health, with the hope that it would encourage people to talk about it openly.

"There's a lot of shame attached to mental illness. You feel like something it's wrong with you," Gaga said to William.

"I should be so happy, but you can't help it when in the morning you wake up, you are so tired, you are so sad, you are so full of anxiety and the shakes that you can't barely think," she continued.

Prince William replied, "It's OK to have this conversation. It's really important to have this conversation. You won't be judged. It's so important to break open that fear and that taboo which is only gonna lead to more problems down the line."

It's so important to break open that fear and that taboo which is only gonna lead to more problems down the line.

William, the Duchess of Cambridge, and Prince Harry are supporters of the Heads Together campaign, which has a goal of ending the stigma around mental health and providing help for people who are dealing with such challenges.

In March, the three royals released 10 short films in support of the campaign, which featured celebrities and members of the public talking about the breakthrough conversation that helped them come to terms with their mental health issues.

Getty Images
Prince Harry, Prince William, Duke of Cambridge and Catherine, Duchess of Cambridge (wearing a giant foam hand) cheer on runners talking part in the 2017 Virgin Money London Marathon on April 23, 2017 in London, England. The Heads Together mental heath campaign, spearheaded by The Duke & Duchess of Cambridge and Prince Harry, is the marathon's 2017 Charity of the Year. (Photo by Max Mumby/Indigo/Getty Images)

In the July issue of GQ U.K., William opened up about how he hopes the stigma around mental illness will end soon, saying, "For goodness sake, this is the 21st century."

"I've been really shocked how many people live in fear and in silence because of their mental illness," Will told the magazine. "I just don't understand it. I know I come across as quite reserved and shy, I don't always have my emotions brewing, but behind closed doors I think about the issues, I get very passionate about things."

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