The royals reunited for the King's very glamorous birthday party at Clarence House on Tuesday evening.
The Prince and Princess of Wales and Charles's nieces, Princess Beatrice and Zara Tindall, were among the guests pictured leaving the private bash to mark his 75th birthday.
But it appears that the King's siblings missed the family gathering due to work commitments.
The Princess Royal carried out engagements in Glasgow, Scotland on Tuesday, ending the day with an appearance at Interfaith Glasgow's Scottish Interfaith Week Forum at Glasgow City Chambers.
Meanwhile, the King's youngest sibling, the Duke of Edinburgh arrived in Singapore on Tuesday morning.
According to the Court Circular, Prince Edward, 59, attended a reception for the Commonwealth Games Federation at Swissȏtel the Stamford.
Edward's wife, the Duchess of Edinburgh, also stepped out for a dinner at Rochester Cathedral on the evening of the party.
It's not known if the Duke of York, who stepped back from public duties in 2019, was among the guests at Clarence House.
Prince Andrew's ex-wife, Sarah, Duchess of York, paid tribute to her former brother-in-law in an Instagram post where she shared a black and white snap of a young Prince Charles.
"Wishing the happiest of birthdays to His Majesty, King Charles III. Long live the King," she wrote in the caption.
© GettyMeanwhile, the Prince and Princess of Wales shared a series of heartfelt images to mark the King's special day.
The snaps showed Prince William and his dad on a previous ski holiday, while another was a solo portrait of His Majesty. A third showed the Wales family with the King and Queen, posing on the balcony of Buckingham Palace at Trooping the Colour earlier this year.
It was very much a working day for Charles on his milestone birthday.
The King and Queen launched the Coronation Food Project as they visited a food distribution hub in Oxfordshire.
The initiative aims to bridge the gap between food waste and food needs across all four nations of the United Kingdom, helping people and helping the planet.
Ahead of his private birthday party, Charles also hosted around 400 nurses and midwives at a Buckingham Palace reception as part of the NHS 75 celebrations.
The King was treated to a surprise performance of Happy Birthday by the NHS choir, with nearly the whole ballroom joining in, before he left the event.
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