Queen Elizabeth II celebrated her 91st birthday on Saturday (17 June) by witnessing her royal guardsman Trooping the Colour at the Horse Guards Parade.

More than 1,000 soldiers performed tightly choreographed manoeuvres in accordance with a tradition stretching back to 1748.

Afterwards, the monarch took to the balcony of Buckingham Palace to watch a Royal Air Force display with members of the Royal Family.

Her great-grandson Prince George, however, was less solemn in his appreciation of the fly-past, as the three-year-old showed signs of boredom as the ceremony concluded.

Of course, it was a very hot day in London and a lot to take in for the third in line to the throne, who turns four on 22 July.

People on Twitter have been pointing out the young prince's facial expressions.

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Britain's Queen Elizabeth II (C) gestures to the crowd as members of the Royal Family leave the balcony of Buckingham Palace after watching a fly-past of aircraft by the Royal Air Force, in London on June 17, 2017.Getty Images
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Members of Britain's royal familly stand on the balcony of Buckingham Palace after Trooping the Colour in London, Britain, June 17, 2017.REUTERS
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Members of Britain's royal familly stand on the balcony of Buckingham Palace after Trooping the Colour in London, Britain, June 17, 2017.REUTERS

Other photographs show him and his younger sister Princess Charlotte hollering with glee as the red arrows performed hair-raising aerial acrobatics over the mall for the delight of his great-grandmother and the thousands of her subjects that flocked to the Mall to wish her a happy birthday.

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Catherine, Duchess of Cambridge, Princess Charlotte of Cambridge, Prince George of Cambridge and Prince William, Duke of Cambridge look out from the balcony of Buckingham Palace during the Trooping the Colour parade on June 17, 2017 in London, England.Getty Images
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Members of the Royal Family (L-R) Britain's Queen Elizabeth II, Vice Admiral Timothy Laurence, Britain's Princess Beatrice of York, Britain's Prince Philip, Duke of Edinburgh, Britain's Catherine, Duchess of Cambridge (with Princess Charlotte and Prince George), and Britain's Prince William, Duke of Cambridge, stand on the balcony of Buckingham Palace to watch a fly-past of aircraft by the Royal Air Force, in London on June 17, 2017.Getty Images
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Members of the Royal Family (L-R) Britain's Princess Eugenie of York, Britain's Queen Elizabeth II, Vice Admiral Timothy Laurence, Britain's Princess Beatrice of York, Britain's Prince Philip, Duke of Edinburgh, Britain's Catherine, Duchess of Cambridge (with Princess Charlotte and Prince George), Britain's Prince Harry and Britain's Prince William, Duke of Cambridge, stand on the balcony of Buckingham Palace to watch a fly-past of aircraft by the Royal Air Force, in London on June 17, 2017.Getty Images

Comparisons were also made to his father William and uncle Harry's reactions during the Queen's birthday celebrations in 1988.

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Princess Diana holds Prince Harry as her older son Prince William (L) looks out over the balcony of Buckingham Palace in London on June 11, 1988 after attending the Trooping the Colour ceremony, the Queen's birthday parade. REUTERS/StringerREUTERS

It was certainly a day for summer attire as temperatures in London reached a sweltering 29C. The heat was so oppressive that a reported five bearskin clad guardsman collapsed while Trooping the Colour.

Queen Elizabeth II, the longest reigning monarch in English history, marked her birthday with an unprecedented speech acknowledging the collective shock felt following three major terrorist attacks committed against Britain in 2017 as well as the recent Grenfell Tower fire.

She said: "During recent visits in Manchester and London, I have been profoundly struck by the immediate inclination of people throughout the country to offer comfort and support to those in desperate need."

"United in our sadness, we are equally determined, without fear or favour, to support all those rebuilding lives so horribly affected by injury and loss," she added.