Welcoming presidents, prime ministers, kings and queens to London, Elizabeth II told her illustrious audience that like her great-grandfather and father before her she would "take pleasure in opening" the Olympic Games in Britain.
Guests including Michelle Obama and Queen Sofia of Spain had been invited to mingle over over canapes at Buckingham Palace before making their way in convoy to the Olympic stadium in Stratford, East London.
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After a day spent jumping around with school children, as part of her Let's Move campaign, the US first lady was the picture of elegance into a white ensemble by J Mendel.
Embroidered with silver thread and featuring capped sleeves, it allowed her to show off the results of her daily 6am workouts.
It was a fitting choice to keep up with Britain's reigning first lady of fashion, the Duchess of Cambridge, who was chic in a mint green coat dress by cutting edge British designer Christopher Kane.
Flanked by Prince William, Kate enthusiastically with Michelle on their second meeting - they were first introduced on the US state visit last year.
The Duchess of Cornwall, accompanying her husband Prince Charles, looked lovely in a cream dress.
Completing the Windsor contingent was the Duke of York and his daughters, Princesses Beatrice and Eugenie, the Earl and Countess of Wessex and the Princess Royal and her husband Vice Admiral Timothy Laurence.
Also on the list of 70 royals and foreign dignitaries was Brazil's President Dilma Rousseff, whose country will host the 2016 Olympics.
The Queen told her guests: "Over recent months, many in these islands have watched with growing excitement the journey of the Olympic Torch around the United Kingdom.
"As the torch has passed through villages and towns it has drawn people together as families and communities.
"To me, this spirit of togetherness is a most important part of the Olympic ideal; and the British people can be proud of the part they have played in keeping the spirit alive.
"Many sports played in these Games have their historic roots in this country; and as a nation we have an abiding passion for sport, as well as a tradition of fair play and a good-natured sense of fun."
A note of pride could be heard in the monarch's voice as she reminded her guests of her family's connection to the Games.
Her great-grandfather Edward VII opened the 1908 Games at White City and her father, George VI, opened the 1948 Games at Wembley Stadium.
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