"Following the news that Prince Charles is set to take over as the Head of the Commonwealth, we have seen a surge of bets on the Queen stepping down from the throne in 2018 where her odds have tumbled in the last 24 hours", John Hill of Coral told Express.
The Queen appeared to be enjoying her birthday celebrations as she was spotted nodding along to a rendition of George Formby's When I'm Cleaning Windows.
Prince Harry and fiancee Meghan Markle also attended, generating a roar of applause when they took their seats. And at that precise moment, Queen Elizabeth's eyes got extremely wide, drawing huge laughs from the crowd.
Elizabeth's real birthday this year came on the tails of the Commonwealth Heads of Government meeting, which brought the leaders of the 53 Commonwealth countries together in England.More news: Saudi Arabia to show 'Black Panther' to mark cinema opening
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Elizabeth was born April 21, 1926, and became queen in 1952 at the age of 25, meaning she has now reigned for more than 66 years.
Prince William was also in attendance, riding in the auto with Harry and Markle, but his wife Kate Middleton, pregnant with their third child, opted to stay home.
Ahead of her celebration, the queen formerly named Prince Charles her successor, putting an end to speculation that she may choose to skip him in favor of his son, Prince William.
While events were held nationwide to celebrate the Queen's 90th birthday, Elizabeth II usually prefers to spend her birthday in private.
A host of stars have entertained the Queen to help celebrate the world's oldest monarch's 92nd birthday.
The Queen also has an "official" birthday in June, which is marked with a large parade of soldiers through central London, known as Trooping the Colour.