The crowd roared with laughter as the Queen momentarily broke the formality at the event to mark her birthday.
Queen Elizabeth is marking her 92nd birthday with a Saturday night concert in London featuring British singers such as Sting, Tom Jones and Jamie Cullum. He joked that she could not have predicted in 1948, when Charles was born, decades later a 92-year-old queen would be sharing a stage with her 70-year-old son.
Meghan's outfit matched with her future husband, who also wore navy for the occasion.
As the audience chuckled, the Queen could be seen rolling her eyes in amusement too.
Celebrating an official birthday as monarch is a practice that started more than 250 years ago in 1748 when King George II decided that he wanted a better chance of good weather on his birthday than his November birth date afforded, according to the BBC. She has also ruled longer than any monarch in the history of Britain.
The members of the royal family included Camilla, Duchess of Cornwall, Princess Eugenie, Princess Beatrice, Prince Charles, Prince of Wales, Lady Louise Windsor, Sophie, Countess of Wessex, Prince William, Duke of Cambridge, Princess Anne, Princess Royal, Vice Admiral Sir Timothy Laurence and Prince Edward were all in attendance.
Another added: "That eye roll from the queen though when Charles called her Mummy".
Queen Elizabeth is the first-ever head of state to open not one, but two Olympic Games in two different countries: Queen Elizabeth helped kick off the 1976 Montreal Games and also made a splashy appearance in the 2012 Summer Games, starring with James Bond actor Daniel Craig in an action-packed short film run during the opening games. The intergovernmental organization was established in that year by King George VI. It usually falls on the second Saturday in June, when she joins the Trooping the Color military parade in central London.