By Nicholas Witchell
Royal correspondent, BBC News
Diana worked at a nursery school before she became a princess
"No-one who ever knew Diana will ever forget her."
So said the Queen in the live broadcast she gave from Buckingham Palace at six o'clock on the evening before the princess's funeral.
It was the moment when Elizabeth II appeared as both monarch and grandmother and broadcast, as she said herself, "from my heart".
On no occasion during her long reign had there been a moment of such drama or poignancy to equal it.
I suspect many of us will be able to remember that broadcast, just as we can still vividly recall so many things about where we were and how we felt as the tragedy of 31 August 1997 and the ensuing days unfolded.
Every bit as significant is what the Queen went on to say in that broadcast about Diana.
"I for one," she said, "believe that there are lessons to be drawn from her life and from the extraordinary and moving reaction to her death."
Those words represented something most unusual.
They were the closest thing to an acknowledgment from the Queen that, in some important respects, she, her family and her advisers had misjudged matters in that tumultuous week after the princess's death.
It was also an acknowledgement they needed, and wanted, to learn from what, in so many ways, had been the extraordinary experience of the life, and tragic death, of Diana, Princess of Wales.
One year after Diana's death, I recall going to a meeting at Buckingham Palace with several of the Queen's most senior advisers.
Charles and Diana announced their engagement on 24 February 1981
Rather, it seemed, to their surprise, they were asked to define what they had gleaned about the "lessons" the Queen had referred to in her broadcast and, further, had those lessons actually been learnt?
There was a pause, a metaphorical shuffling of the feet and clearing of throats, which was followed by phrases such as: "continuing evolution...", "a gradual..." this and that, and so on.
Poor old Buckingham Palace - it always appeared to struggle somewhat in dealing with Diana Spencer.
It struggled in the days immediately after her death, when the Queen and at least one of her shrewdest courtiers - Robin Janvrin, who was unfairly portrayed in the otherwise perceptive film The Queen - were cocooned at Balmoral in the Scottish Highlands.
Where, understandably, the priority was to deal with a family tragedy that had robbed two boys, then aged 15 and 12, of their mother.
And it continued to have difficulty in the months that followed, as it attempted to fulfil the Queen's wish, and assimilate - as the monarch herself had put it - the "lessons" to be drawn from Diana's life and the "extraordinary" reaction to her death.
Anger and guilt
There is no doubt the palace had been massively wrong-footed by the sheer emotional intensity of the public response to Diana's death.
Alongside the inevitable shock and grief at the sudden extinction of such a young and vital life there was a strong element of anger.
And, perhaps, buried somewhere within the many layers of emotion, there was also a little guilt that, somehow, we had all played a part in demanding far too much from this young woman.
What particularly disconcerted the palace, of course, was the way in which this whirlpool of feelings found such ready expression in hostility towards the Royal Family.
Diana and Dodi Al Fayed planned to dine out after calling into the Ritz
At that moment of national grief, the Queen and her family were perceived by many to be demonstrating precisely those characteristics which, so it was thought, had driven this beautiful young woman to distraction.
The royals appeared to many to be aloof, cold and uncaring.
All of which placed the Royal Family and their senior advisers in the place they least like to be - in unfamiliar territory.
All of their contingency plans based on precedent and rooted in protocol, all of their long-held and reassuring assumptions about a stoical, loyal population seemed, suddenly, to be being turned upside down by tremulous, resentful crowds whose lips were quivering and fingers waving in the direction of Buckingham Palace.
That week, at the beginning of September 1997, and in the months that followed, courtiers had to do something that many of them, instinctively, find rather difficult. They had to improvise and experiment.
One of those who found herself in that position was Mary Francis.
In the autumn of 1997, she was one of the Queen's private secretaries, the small group of senior advisers who offer daily advice to the monarch.
Speaking to me a few days ago, Ms Francis recalled the time after Diana's death. She described it as a potentially damaging week when the Royal Family and its advisers were forced to learn some "harsh lessons" about the need for them to be seen, more effectively, to be in tune with the public mood.
She believes those lessons have been learnt and that we have a royal family that is more receptive and open than it was before.
Diana's most obvious legacy is her sons. They will shape the future of the British monarchy and they will do so, at least in part, in her image.
Princess Diana's funeral was watched by 31 million people
But at the moment of her death, this princess, who had always kicked against the stuffier side of palace protocol, caused events to occur that shook the stuffier elements of the existing monarchy to its somewhat stultified roots.
The institution was jolted out of its complacency and forced to look at itself with a very much more critical eye.
Subtle changes in style and approach - some of which had already started prior to the princess's death - were brought forward with greater speed than might otherwise have been the case.
In fairness though, it must be said that, ultimately, a potentially menacing moment for the British monarchy was rescued, 10 years ago, by the monarch herself.
It may indeed have been the Queen who, initially, placed far too great a reliance on protocol to see them through, and who may indeed have needed some gentle prodding from Downing Street and elsewhere before she realised the full scale of the national trauma.
But once she had broken out from the family sadness of Balmoral, it was the Queen who led the tributes and who, most importantly, recognised the need for the ancient institution she heads to learn from the young princess whom it had so recently banished.