The King will mark his 75th birthday on Tuesday 14 November, with Charles reportedly set to celebrate his milestone during a private family party at Clarence House.
The Prince and Princess of Wales, the Princess Royal and the Duke and Duchess of Edinburgh are likely to be among the guests in attendance, as well as extended members of the King's family.
While it's likely to be an intimate affair, if Charles's 70th birthday celebrations are anything to go by, it could mean a black-tie dress code.
That means tuxedos for the royal gents and evening dresses for the ladies, as well as some showstopping jewels.
The late Queen Elizabeth II hosted a bash at Buckingham Palace for then Prince Charles's 70th birthday in 2018.
While the party took place privately, several members of the royal family were seen arriving at the palace in their cars.
The then Duchess of Cambridge stunned in a pink one-shoulder gown with jaw-dropping morganite earrings.
Newlyweds Princess Eugenie and Jack Brooksbank were also spotted arriving, with Eugenie sporting a strappy teal blue dress.
Eugenie's sister, Princess Beatrice, arrived separately and appeared to be wearing a semi-sheer blue dress with large statement earrings.
The Duke and Duchess of Sussex had just returned from their first major royal tour, with Prince Harry driving his then pregnant wife Meghan to the palace.
Buckingham Palace also released a photograph of Charles and Camilla from inside Clarence House before they left for the party.
It showed the then future King wearing a tuxedo while his wife looked elegant in a midnight blue pleated gown with diamond jewellery.
The palace is yet to formally announce plans to mark Charles's 75th birthday.
It has been a busy few weeks for the King and Queen following their first state visit to Kenya at the beginning of November.
Charles also delivered his first ever King's Speech at the State Opening of Parliament on Tuesday, and in the evening he and Camilla enjoyed a night out at the ballet at the Royal Opera House.
From 21 to 23 November, the King and Queen will host The President of the Republic of Korea, His Excellency Yoon Suk Yeol, and First Lady Kim Keon Hee during their state visit to the UK.
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