In the image, which can be seen below, the King looked incredibly proud as he sat in a suit and tie and was adorned with a golden robe as he carried out rehearsals for his coronation, the first in Britain for 70 years. The photo was taken in Westminster Abbey and features the King sat in his coronation chair.
The one-off 90-minute documentary, titled Charles III: The Coronation Year will air as part of the BBC's festive schedule next month and camera crews were given exclusive access to the King and his wife Queen Camilla for the episode.
The special will chart the "landmark moments" in Charles's first year as monarch including the run-up to his coronation, the ceremony itself and events that took place in the months after. Members of the Royal Household and the royal family have contributed to the special.
Some of the moments include the state visit from South Africa's president, Cyril Ramaphosa, the King leading the nation in mourning for his late mother, the Queen, and at Remembrance Sunday services, Trooping the Colour and his first state visit as monarch to Germany.
In a statement, the BBC said that the documentary will feature "moments of great poignancy and humour" and will offer a "unique perspective on the inner workings behind a defining moment which marks a new era in the history of the monarchy".
Simon Young, the BBC's head of history and factual commissioning, said: "At the heart of this story is a man who is taking on the job that has always awaited him. Everyone wants to know how he takes on that challenge. This film captures a behind the scenes view of the King and his coronation the like of which has never been seen before."
The news comes shortly after an important moment for the King, as he hosted South Korea's president Yoon Suk Yoel during the politician's state visit to the UK this week.
One of the highlights of the trip was a state banquet that was hosted on Tuesday evening. Charles, 75, and Camilla, 76, were joined by the Prince and Princess of Wales, the Duchess of Edinburgh and the Princess Royal for the white-tie dinner.
The King wore a white tie with decorations and a full set of miniature medals, as well as the Garter Star and the Thistle Star, which used to belong to his grandmother, the Queen Mother.
He also sported the Grand Order of Mugunghwa – the highest national order awarded by South Korea – which was presented to him by President Yoon Suk Yeol at the exchange of gifts on Tuesday at Buckingham Palace.
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