The King celebrated his 75th birthday a day early after he was presented with a three-tiered cake at a party attended by friends and celebrities.
Charles joined a host of people, from community stalwarts nominated by friends and family who are also turning 75 this year, to representatives from organisations marking the same milestone, from the NHS to members of the Windrush generation.
Among the famous faces at the event on the grounds of the King's Highgrove home in Gloucestershire were celebrity chef Raymond Blanc, The Repair Shop host Jay Blades and singer Leee John from the 1980s group Imagination.
A local choir sang Happy Birthday for the head of state at the end of the cream tea party, and after debating which of the three tiers of the Victoria sponge to cut Charles opted for the bottom.
He was cheered and applauded after cutting a slice and holding up the knife in celebration and peering at the sweet treat.
Tuesday will be a normal working day for the monarch, who was born on November 14, 1948, and he is set to officially launch the Coronation Food Project with Queen Camilla, which aims to bridge the gap between food waste and food need.
Charles will host a Buckingham Palace reception to celebrate nurses and midwives as part of the NHS 75 celebrations.
Gun salutes will also be fired across the capital and the nation to mark the King's milestone.
Mr Blades, an ambassador for the King's Foundation, paid tribute to Charles, saying: "He's the new King but he's also about community, he's always been about community, always been forward thinking about what we're doing about the environment but also including community members.
"So to have this group of people here, that's just unbelievable - that's part of him, that's what he does."
At Dumfries House in Scotland, the home of the King's Foundation, a similar gathering of community figures to mark the King's birthday was held.
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