During her 70-year reign, Queen Elizabeth II broke royal protocol just once in what became a very famous moment in history, which has resurfaced following her death at age 96.
As the head of the monarch, the Queen was never required to bow her head or curtsy to anyone, with the Queen often the recipient of such gestures from people showing her respect.
However, there was one time the Queen broke that royal rule and bowed her head to pay her respects to the late Princess Diana - an act she was only ever seen doing once during her reign.
At Princess Diana's funeral on September 6, 1997, the Queen bowed her head as Diana's coffin passed her on a gun carriage.
The host of Italian documentary series Ulisse, Alberto Angela, said the death was one of the Queen's most profound moments.
"There is an image captured on the day of Diana's funeral which is highly symbolic," he said in the series.
"We are in front of the Buckingham Palace gate. It is known that before the Queen, who is the symbol of national unity, everyone bowed.
"But that day, it is Elizabeth who bowed her head as a sign of respect for the passage of Diana's coffin, the woman who wore more than anyone else had defied the conventions of the palace."
He said the image of the Queen bowing her head to the late Diana was possibly one the "strongest" images captured during her reign.
"Even in the darkest hour, Elizabeth put her mission first and demonstrated that she can find inspiration even from the most painful confrontation, the one with the woman who had won the hearts of her subjects," he said.
He added the monarchy "came out even stronger" from that one dramatic moment.
The moment came after the Queen sparked public outcry when she initially refused to make a public address about Diana's death, but the Queen later relented.
In an address to the nation following Diana's death, the Queen said it was not easy to express a "sense of loss".
Speaking about feelings of disbelief, incomprehension, anger and concern for those Diana left behind, the Queen said they had all felt those emotions.
"What I say to you now, as your Queen and as a grandmother, I say from my heart," she said.
"First, I want to pay tribute to Diana myself. She was an exceptional and gifted human being. In good times and bad, she never lost her capacity to smile and laugh, nor to inspire others with her warmth and kindness.
“I admired and respected her — for her energy and commitment to others, and especially for her devotion to her two boys."
She added there were lessons to be drawn from Diana's life and her memory would be cherished.
The Queen dies aged 96
The Queen’s death was announced by Buckingham Palace on Friday morning AEST.
Their statement said: “The Queen died peacefully at Balmoral this afternoon. The King and The Queen Consort will remain at Balmoral this evening and will return to London tomorrow.”
Charles quickly issued his own statement, saying: “The death of my beloved Mother, Her Majesty The Queen, is a moment of the greatest sadness for me and all members of my family.”
“We mourn profoundly the passing of a cherished Sovereign and a much-loved Mother. I know her loss will be deeply felt throughout the country, the Realms and the Commonwealth, and by countless people around the world.
“During this period of mourning and change, my family and I will be comforted and sustained by our knowledge of the respect and deep affection in which The Queen was so widely held,” he finished.
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