Kate Williams is a professor of history at the University of Reading, the author of "Young Elizabeth" and a CNN royal commentator and contributor. The views expressed in this commentary are her own.

(CNN) In the early hours of August 31, 1997, the media began reporting that Diana, Princess of Wales, had been injured in a car crash in the Pont l'Alma tunnel in Paris. By 4:45 am, news channels were citing sources who claimed Diana had died .

Members of Britain's royal family were on their annual summer break at Balmoral Castle in Scotland. They issued a statement at 5:25: "The Queen and Prince Philip are deeply shocked and distressed by this terrible news. Other members of the royal family are being informed of the Princess's death."

They thought this would be enough.

But the royals made a grave error in how they reacted to the news of Diana's death -- one that lost them public respect at the time and has taken nearly two decades to regain.

As the news spread, a wave of grief swept across the world , taking everyone by surprise -- most of all the royals. Politicians struggled for the words to describe her death. Her brother, Earl Spencer, paid tribute from South Africa and talked about how it seemed as though the press had taken "a direct hand in her death." And Prime Minister Tony Blair began referring to her as the "People's Princess."

The royals, other than releasing an initial brief statement, stayed silent and remained in Balmoral.

As far as they were concerned, Diana simply wasn't part of the family anymore. She had divorced Prince Charles and given up the title of her royal highness. In their view, the routine and the behavior that would follow if a senior member of the royal family had died simply did not apply here.

Where the royals went wrong

The Queen 's attitude in moments of crisis has always been "keep calm and carry on." It has stood her well through a turbulent life -- her uncle's abdication, World War II, her father's early death and her abrupt accession to the throne.

But in this crisis, it was an error. People felt the royals were insulting Diana -- and even royalist newspapers, such as the Daily Express, demanded her presence in London. As they put it: " Show us You Care.

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To the public, Diana was a princess and mother of the future king. As many saw it, she had been poorly treated by the royals and Charles -- and the royal response to her death only made things worse.

Politicians and courtiers, who could sense the growing resentment, pushed the royals to take further action -- and a ceremonial funeral was planned.

The Queen went on television on the eve of the funeral to give a deeply emotional address, telling everyone how members of the royal family had been grieving, how they had been focusing on the princes.

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She praised Diana's gifts and addressed the nation "as a grandmother." It was an alien way of speaking for the Queen -- a war child who kept her emotions to herself.

However, the most memorable words of the funeral and that period were not the Queen's, but the funeral oration of her brother, who spoke of his family's grief and talked of how Diana was "a symbol of selfless humanity" and a "standard bearer for the suffering."

He pointed out the horrific irony that the girl given the name of the Roman goddess of hunting "became the most hunted person of the modern age," and ended by telling the world her "beauty, both internal and external, will never be extinguished in our minds."

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The funeral borrowed from plans set aside for the funeral of the Queen Mother. But there was no lying in state -- whereas the Queen Mother would lie in state for three days in Westminster Hall on her death in 2002 and more than 200,000 people visited.

Strictly speaking, this was only for the monarch and the queen consort, or the wife of a king, as well as some prime ministers. However, many Brits thought Diana would one day have been the queen consort, and so she deserved it. Certainly, a lying in state, even for a day, would have gone some way toward appeasing the public anger. The princes were also told by the palace that they had to walk behind their mother's coffin. Earl Spencer objected to this order, saying, "Diana just would not want them to do this." But he was, as he said earlier this year, "'lied to" and told that walking was the princes' wish.

Prince Harry reiterated as much and told Newsweek magazine this year, "I don't think any child should be asked to do that, under any circumstances."

Twenty years later

In the immediate aftermath of Diana's death, the royal family had made a grave mistake -- and though the Queen's words on the eve of the funeral and the funeral itself helped to improve the royals' standing a bit -- it would take some time before the country could forgive them.

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Twenty years have passed since Diana's death, and her sons are carrying on her legacy. Diana has been commemorated this year by a private ceremony at her family estate, Althorp, in a service led by her brother and attended by the princes.

And although the royal family has regained some popularity, it is the Queen, the Duke and Duchess of Cambridge, and Prince Harry who are widely admired.

Charles, it seems, cannot connect with the public and press coverage of his visits is very low, compared with the flurry of attention over William and Catherine. A recent poll suggested that only a third of Britons felt that Prince Charles had been beneficial to the monarchy.

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But even the other members of the royal family cannot rely on the affection of the British people. The pendulum of public opinion can easily turn the other way, if and when the next crisis arises.

The hope of Charles and his inner circle is that when he ascends the throne, the mistakes of the 1990s will be forgotten. But, even today, Diana is still present in the public imagination. And the royal family will always be seen, and perhaps even judged, in terms of her life and death.