He is now back in the UK, where, he was spotted attending church at Sandringham in Norfolk on Sunday.
The monarch could be seen bundled up in a long tan coat as he wrapped up warm against the cold weather and strolled to the morning's service alongside his wife, Queen Camilla.
The Queen coordinated with her husband, wearing a light brown coat and sporting a scarf and hat in matching shades. While Charles at times appeared deep in thought, Camilla turned and smiled at the camera in between talking to her husband.
The pair were greeted by Reverend Canon Paul Williams as they made their way to St Mary Magdalene Church. The King's visit comes after the release of Omid Scobie's latest release Endgame, which makes a number of claims about the royal family, including alleging a rift between King Charles and his eldest son, the Prince of Wales.
The book, which was published on Tuesday, looks at the current state of the British monarchy and what it "must change in order to survive".
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It claims: "He's [William] not giving his father the same space Charles did with the Queen. There's no time for that." Mr Scobie told The Times in a recent interview: "It would have been nice to see them come together on certain projects perhaps in the early years, to put on that united front, but they’re all working in silos."
HELLO! has reached out to the Duke and Duchess of Sussex's representatives. Buckingham Palace and Kensington Palace have declined to comment.
Last weekend, the King made the trip to church on his own, following sad news earlier in the week. The monarch was mourning the sad loss of a family friend: Queen Elizabeth II's loyal companion and former lady-in-waiting, Prudence, Lady Penn.
Lady Penn, also known as Prue, was the widow of Sir Eric Penn, the one-time Comptroller of the Lord Chamberlain's Office. Over the years, when she lived very close to Buckingham Palace, Prue had become a close confidante and family friend of the royals.
Aside from forming a friendship with Queen Elizabeth II, Lady Penn also enjoyed a close bond with Princess Margaret and the Queen Mother. When Charles became King, she confided to a friend on his Accession: "Have you noticed how our new Sovereign seems to have grown in stature overnight? He looks every inch a king.
"I am devoted to him and know that he will take on the mantle with sensitivity, wisdom, and strength." Lady Penn was also appointed LVO in the 2002 demise honours list. She is survived by her two sons and a daughter.
Sandringham is where the late monarch typically spent her winter break, residing there throughout the festive period before returning to London after the anniversary of her father King George VI's death on 6 February.
Since her death, the King has continued his mother's tradition of spending Christmas at the estate, and attending church with his family on Christmas Day.
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