This marks the second birthday Charles has celebrated on the British royal throne.
King Charles III is ringing in a milestone birthday with some social media love from several members of his family.
Charles' eldest son, Prince William, and his wife, Kate Middleton, took to their official account to post several sweet throwback photos with the monarch, writing, "Wishing His Majesty The King a very happy 75th birthday! 🎂"
In one pic, a much younger William has his arm around his dad on a skiing holiday as the two are all smiles.
William and Kate also shared a photo from the 2023 Trooping the Colour official fly over at Buckingham Palace with their three children, Prince George, Princess Charlotte, and Prince Louis, and Charles and Queen Camilla.
And the Prince and Princess of Wales weren't the only members of the royal family to wish Charles a happy birthday. Sarah Ferguson (a.k.a. Fergie) also took to X (formerly Twitter) to share a black-and-white throwback photo of Charles, writing, "Wishing the happiest of birthdays to His Majesty, King Charles III. Long live the King."
Fergie is the ex-wife of Prince Andrew, Charles' younger brother, and the mother of Princess Eugenie and Princess Beatrice.
The official Royal Family account also shared a sweet birthday slideshow of images of the king, including several with his late mother, Queen Elizabeth II.
Charles and Camilla spent the day at the Coronation Food Project where he was treated to a special rendition of "Happy Birthday" by the staff in attendance.
Following a report from The Sunday Times that stated Prince Harry, 39, and Meghan, 42, had turned down the chance to visit the U.K. for his father's birthday, a rep for the Duke and Duchess of Sussex has denied that they declined to appear. In their story, The Sunday Times reported that King Charles celebrated his 75th birthday at Clarence House last weekend.
"In response to U.K. media headlines, there has been no contact regarding an invitation to His Majesty’s upcoming birthday. It is disappointing the Sunday Times has misreported this story," a spokesperson for Harry and Meghan said.
Earlier this year, the second-born son of King Charles and Princess Diana released his memoir, Spare, which detailed his struggles with royal life and his decision to step back from their royal duties.
Around the same time as the book's publication, Prince Harry and Meghan were reportedly asked to vacate Frogmore Cottage on the grounds of Windsor Castle. The cottage had been gifted to them by the late Queen Elizabeth II.
A source told ET in January that "since Harry's book was released, relationships between Harry and Meghan and the family have never been worse."
The couple officially stepped down as senior members of the royal family in 2021, a year after originally making the decision.
The parents of son Archie, 4, and daughter Lilibet, 2, are currently living in California.