Kate Middleton and Prince William Kick Off Tributes for King Charles' 74th Birthday

LONDON, ENGLAND - SEPTEMBER 28: (L-R) Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Camilla, Duchess of Cornwall and Prince Charles, Prince of Wales attend the "No Time To Die" World Premiere at Royal Albert Hall on September 28, 2021 in London, England. (Photo by Karwai Tang/WireImage)
LONDON, ENGLAND - SEPTEMBER 28: (L-R) Catherine, Duchess of Cambridge, Prince William, Duke of Cambridge, Camilla, Duchess of Cornwall and Prince Charles, Prince of Wales attend the "No Time To Die" World Premiere at Royal Albert Hall on September 28, 2021 in London, England. (Photo by Karwai Tang/WireImage)
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Karwai Tang/WireImage

Happy birthday, King Charles III!

Prince William and Kate Middleton released a special message to commemorate the monarch's 74th birthday on social media Monday. The Prince and Princess of Wales, both 40, were the first members of the royal family to do so.

"Wishing His Majesty The King a very happy birthday today," the post read, accompanied by a smiling shot of the King. The image was taken during his visit to Yorkshire last week, where he toured Morrisons Supermarkets headquarters to learn more about the grocery hub's sustainability initiatives and apprenticeship programs.

Buckingham Palace similarly wished Charles a happy birthday Monday, tweeting another smiling photo of the sovereign along with a peek behind the scenes of related tributes in London. The King's Troop Royal Horse Artillery fired cannons in Green Park at midday, and the Household Cavalry Band delivered an epic rendition of "Happy Birthday" during the Changing the Guard ceremony outside Buckingham Palace.

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Charles has previously hinted that he's lighthearted about the idea of growing older. Last month, the King had the perfect reply for a curious schoolchild who wondered aloud how old he was during a stop in East London.

As seen in a video shared to Twitter by Sky News' Rhiannon Mills, the King was chatting with young pupils queued outside Project Zero Walthamstow when one student asked, "How old are you, King Charles?"

"You can have a guess, you can have a guess," the monarch replied with a laugh.

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This is Charles' first birthday since acceding as King following the death of his mother Queen Elizabeth in September. While his coronation has been set for May 6, the palace has yet to release details about a Trooping the Colour celebration in his honor, as his mother did as monarch for 70 years before him.

Prince Charles, Prince of Wales poses for an official portrait to mark his 60th birthday, photo taken on November 13, 2008 in London, England.
Prince Charles, Prince of Wales poses for an official portrait to mark his 60th birthday, photo taken on November 13, 2008 in London, England.

Hugo Burnand-Pool/Getty King Charles III

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In a twist of history, King George II kicked off the summer tradition — a military parade in the monarch's honor — because, like Charles, his birthday was in the chilly month of November, according to Royal Museums Greenwich. In modern custom, Trooping the Colour has been held on the second Saturday in June.