King Charles was seen greeting the public as he arrived at Clarence House on Tuesday afternoon.
The monarch, 75, had been at Windsor Castle this morning but left before the memorial service for his second cousin, King Constantine of Greece, began.
The King has not performed public duties since being diagnosed with an unspecified form of cancer on February 5.
His wife, Queen Camilla, led the British royal family during her and Prince William’s absence while Her Majesty returned to London.
Her Majesty could be seen wiping away tears at the service to Constantine II of Greece, who died in January 2023 and was William’s godfather.
No details have been given about Prince William’s absence and it is not known if it is related to his wife Kate Middleton’s ongoing recovery following her abdominal surgery last month.
King Charles was seen greeting the public as he arrived at Clarence House on Tuesday afternoon.
The King had been at Windsor Castle earlier today, but left before the memorial service began.
Pictured: King Charles III attends the Sunday service at St Mary Magdalene Church on the Sandringham estate on February 18.
Queen Camilla wipes away a tear at the funeral for the life of King Constantine.
Pictured: Guests attend a service of thanksgiving for the life of King Constantine of the Hellenes at St George’s Chapel, Windsor Castle, Berkshire.
Pictured: LR The Duke of Gloucester, Admiral Sir Tim Laurence and the Princess Royal join (second row from left) Edoardo Mapelli Mozzi, Sarah Duchess of York, Lady Helen Taylor and the Duke of Kent attend a service of thanksgiving for life. of King Constantine of the Hellenes
Pictured: Left to right: Queen Anne Mary of the Hellenes, Crown Prince Pavlos of Greece and Crown Princess Marie-Chantal of Greece attend a service of thanksgiving for the life of King Constantine of the Hellenes in St. George’s Chapel, Windsor Castle.
It comes as a Greek Orthodox monk claimed King Charles had turned to him for spiritual advice since being diagnosed with cancer.
It is claimed that the king secretly contacted Archimandrite Ephraim, who was said to have been a friend for over 25 years.
The king and the abbot are understood to have become close after Princess Diana’s death in 1997.
The Prince of Wales, who was due to give a reading, called the family to apologize, while Kensington Palace confirmed Kate was “doing well” as she recovers at home.
Kate will stay away from official royal engagements until after Easter following her surgery.
Prince Andrew was present today with Sarah, Duchess of York and their daughters, Princess Eugenie and Beatrice, because it was considered a personal family event.
It is also understood that the Duke of York was attending the service as a member of the British royal family and had been invited by the Greek royal family.
Pictured: LR Lord Cavendish of Furness, US climate envoy John Kerry and Dame Norma Major.
Pictured: Prince Andrew, Duke of York, attends a service of thanksgiving for the life of King Constantine.
In the photo: Crown Prince Alexander of Serbia and Princess Catherine of Serbia.
Pictured: Zara Tindall attends a service of thanksgiving for the life of King Constantine of the Hellenes.
In the photo: Prince Pavlos, Crown Prince of Greece, Prince of Denmark RE, and Marie-Chantal, Crown Princess of Greece, Princess of Denmark (both in front) and Prince Philip of Greece and Denmark (fifth from the right) attend the thanksgiving service.
Queen Noor of Khorndania and Kyril of Bulgaria and Dax Miller and Alexandra von Furstenberg attended the thanksgiving service today.
Pictured: Birgitte, Duchess of Gloucester and Prince Richard, Duke of Gloucester.
Pictured: Jackie Stewart arrives to attend a service of thanksgiving for the life of King Constantine of the Hellenes.
Charles was unable to attend Constantine’s funeral in Athens last year due to commitments that included meeting the president of Cyprus. The Princess Royal represented him at the service.
Constantine, who died in an Athens hospital, acceded to the throne at the age of 23 in 1964.
The young king, who had won Olympic gold in sailing, initially enjoyed great popularity.
By the following year, he had squandered much of that support by actively participating in the machinations that toppled Prime Minister George Papandreou’s popularly elected Center Union government.
The episode, still widely known in Greece as the “apostasy” or defection from the ruling party of several politicians, destabilized the constitutional order and led to a military coup in 1967.
Meanwhile, the Princess of Wales is understood to be “doing well” as she recovers from abdominal surgery.
Earlier this month, The Daily Mail exclusively revealed that Kate joined Prince William and their three children for a half-term holiday at the Sandringham estate in Norfolk.
“Catherine is recovering well,” a friend told the Journal’s editor, Richard Eden.
“He was looking forward to a change of scenery and will be able to take it easy in Norfolk while the children blow off some steam with William.”
When news emerged that Kate had been discharged, a Kensington Palace spokesperson said: “The Princess of Wales has returned to her home in Windsor to continue her recovery from surgery.” She is making good progress.
‘The Prince and Princess would like to say a huge thank you to all the team at The London Clinic, especially the dedicated nursing staff, for the care provided.
“The Wales family remains grateful for the well wishes they have received from around the world.”