Queen Camilla is set to lead memorial for Charles’ second cousin King Constantine of Greece at Windsor Castle – but the cancer-stricken monarch will be absent.
The service is expected to include many of the royal family alongside several of the ruling houses of Europe including the former King of Spain.
The last King of Greece died on January 10 last year at the age of 82 after months of illness – more than 50 years after he was exiled in a military coup.
The royal, the only son of King Paul and Queen Frederica, was nephew to the late Duke of Edinburgh and godfather to Prince William.
His funeral was attended by Princess Anne, who was the late monarch’s second cousin, and her husband Vice Admiral Sir Timothy Laurence.
He became King of Greece in 1964 but was ousted from the throne when the monarchy was abolished in 1973.
King Charles is not expected to attend his memorial in Windsor after drawing back from public life following his cancer diagnosis.
King Constantine II of Greece, King Charles and Queen Camilla attend Sunday service at the Church of St Mary Magdalene on the Sandringham estate in 2007
Camilla’s role in the service will see her again taking the reigns as she works to take the pressure off her husband
Princess Anne cut a sombre figure as she consoled Crown Prince Pavlos of Greece (pictured right) at his father King Constantine’s burial ceremony
Charles’ profound sense of duty and strong work ethic has seen him continue working privately through treatment.
But the monarch was pictured carrying out royal duties for the first time last week as he carried out his first audience of the year with Prime Minister Rishi Sunak.
Camilla’s role in the service will see her again taking the reigns as she works to take the pressure off her husband.
Members of the Royal family have rallied around the King, with Prince William returning to duties after spending time caring for his wife Princess Kate.
In a separate health scare, the Princess of Wales had been admitted to The London Clinic for planned abdominal surgery, and she will not be able to perform any royal engagements until at least Easter.
Last month the Greek royal family put on a sombre display as they attended a memorial service to mark one year since the death of King Constantine.
High-profile royals, including Constantine’s son Crown Prince Pavlos and widow Queen Anne Marie, attended a private ceremony at the former summer palace of Tatoi, just outside Athens.
His public funeral the year before was followed by a 29km procession to Tatoi Palace, where a separate private ceremony was held, before Constantine was laid to rest with other members of the Greek royal family.
Pavlos, Crown Prince of Greece (centre L) and Prince Nikolaos of Greece and Denmark (centre R) carrying the coffin of the late former King of Greece Constantine II, during the burial ceremony, at the Tatoi estate, north of Athens
Crowds gathered around Tatoi chapel during the private burial of the King Constantine II of Greece
Dressed in black, Prince Pavlos, 56, led the way as they gathered together in unity in a service that saw the family placing traditional laurel wreaths on Constantine’s tomb.
The Greek royal family now mainly live in New York, but split their time between the Big Apple, London and Greece.
Following Constantine’s death last year, members of the public queued through the night to see him lying in state.
They then also attended the private burial ceremony at Tatoi, where she offered her condolences to Constantine’s sons, Pavlos and Nikolaos.
Also present at the Orthodox Metropolitan Cathedral funeral service were Queen Letizia of Spain, King Willem-Alexander and Queen Maxima of the Netherlands and King Philippe and Queen Mathilde of Belgium.
Prince William, 41, held an investiture ceremony at Windsor Castle earlier this month before attending London’s Air Ambulance charity gala dinner later that evening.
Last week he attended the BAFTA awards and met with filmmakers and stars, as well as congratulating awards winners, before giving out more awards at a second investiture today.
King Charles met with Prime Minister Rishi Sunak at Buckingham Palace, with the pair seen smiling during their first face-to-face meeting since the monarch’s cancer diagnosis
King Charles and Queen Camilla smile and wave to wellwishers as they attended church at Sandringham on Sunday February 18
Former Chancellor Sir Sajid Javid was also among those to be knighted by the Prince of Wales for his services to politics and public life, while Game of Thrones actress Emilia Clarke and her mother were handed MBEs for setting up a brain injury charity.
However William’s father is said to be supportive of him putting his own family first, and taking time out of engagements to look after his wife and children.
It is understood he visited his father at Sandringham for a half-term holiday along with Kate and their three children, Prince George, Princess Charlotte and Prince Louis.
A source said: ‘The King adores Catherine and thinks she is doing a wonderful job. He understands that family comes first.’
Meanwhile the King was visited in London by Prince Harry, who cleared his diary to fly over from his California home in Montecito while leaving wife Meghan Markle and his two children, Prince Archie and Princess Lillibet, behind.
The Duke of Sussex, 39, flew to London on a commercial plane the day after the announcement, arriving at Clarence House in the afternoon.
He is then thought to have spent around 45 minutes with his father, seeing him for the first time since the late Queen Elizabeth II’s funeral.
Harry is not believed to have seen his brother, with the rift between Charles’ sons showing few signs of ever repairing.
The prince then stayed overnight in a hotel before flying home the next morning.
Meanwhile King Charles and Queen Camilla were driven straight from their meeting with Harry to Buckingham Palace, where they took a helicopter to their Sandringham estate.
Harry is expected to return to Britain in May for a service at St Paul’s Cathedral to mark the tenth anniversary of the Invictus Games.
In an interview with Good Morning America, Harry said he was pleased to have visited the UK to see his father.