Constantine, who was a second cousin of King Charles, a first cousin of the late Duke of Edinburgh, and a godfather to Prince William, enjoyed a close relationship with the British royals.
The memorial service to celebrate his life was held at St George's Chapel on Tuesday morning, with Camilla stepping in for her husband Charles, who is unable to attend due to his ongoing cancer treatment.
Prince William had also been due to attend, but pulled out last-minute due to a "personal matter". He was expected to give a reading, but Constantine's son Crown Prince Pavlos did the honours instead.
Queen Camilla
Queen Camilla stepped in for her husband King Charles, who was unable to attend the memorial due to his cancer treatment.
Princess Anne and Queen Camilla
Queen Camilla was seated next to Princess Anne. The service, which took place in the nave of St George's Chapel, was led by the Dean of Windsor, The Right Reverend Dr Christopher Cocksworth.
British royals
Several members of the British royal family were in attendance.
Mike and Zara Tindall
Mike and Zara Tindall seen walking to the service with Princess Anne.
Duke of Kent
The late Queen's cousin, Prince Edward, Duke of Kent attended the service with his daughter Lady Helen Taylor. His wife, Katharine, Duchess of Kent, who turned 91 last week, rarely attends public engagements.
Prince and Princess Michael of Kent
Prince and Princess Michael of Kent were among the guests. The couple were very close to King Constantine, choosing him as one of their daughter Lady Gabriella Kingston's godparents.
Lady Sarah Chatto
King Charles' cousin, Lady Sarah Chatto, was pictured arriving at the chapel with Princess Anne, Mike and Zara Tindall and Princess Beatrice
Spanish royals
King Constantine's nephew King Felipe of Spain and his wife Queen Letizia were among those to attend the special service.
Crown Prince Pavlos and Crown Princess Marie-Chantal
Royals from the UK and Europe flocked to Windsor for the event, given Constantine's expansive links with other European royal families. His eldest son Crown Prince Pavlos, along with Pavlos' wife Crown Princess Marie-Chantal, led the Greek royals in attendance.
Princess Nina and Prince Philippos
Constantine's son Prince Philippos and his wife Princess Nina were also pictured arriving at the chapel.
Constantine is also survived by his other children: Princess Alexia, Prince Nikolaos, Princess Theodora.
The Duke and Duchess of Gloucester
Prince Richard and Duchess Birgitte also represented the British royal family.
Prince Andrew and Sarah, Duchess of York
Prince Andrew and his ex-wife Sarah Ferguson, who live close by in Windsor, also paid their respects.
Constantine's elder sister was Queen Sofia of Spain.
Representing the Spanish royals were Sofia's daughters Infanta Elena and Infanta Cristina, as well as Cristina's eldest child, Juan Valentin Urdangarin.
King Felipe
Juan Carlos I and his son King Felipe seen leaving the Thanksgiving Service together.
Constantine died at the age of 82 in January 2023. He had been suffering from ill health for a number of years and was treated at the private Hygeia Hospital in Athens.
His funeral took place at the Metropolitan Cathedral in Athens, with a whole host of European royals in attendance, including Princess Anne and her husband Vice Admiral Sir Timothy Laurence, who were representing King Charles and Queen Camilla, and Lady Gabriella Windsor, who was there on behalf of Prince William. Gabriella counted Constantine as one of her godfathers.
William had a "private" engagement on the day of the funeral, while Charles and Camilla had a scheduled meeting with the President of the Republic of Cyprus.
Other European royals in attendance at the funeral included King Willem-Alexander and Queen Maxima of the Netherlands, Prince Albert of Monaco, King Felipe of Spain's sister Infanta Cristina, Queen Mathilde and King Phillipe of Belgium, and Queen Silvia and King Carl XVI of Sweden.
Constantine was later buried at Tatoi Palace cemetery, close to Athens.
Constantine acceded to the Greek throne in 1964 following the death of his father, King Paul I. He was proclaimed King of the Hellenes at the age of 24, however, he ruled for only a decade after a military junta abolished the monarchy. He was the last king of Greece.
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Two referendums were held, a disputed one in 1973 before a second one in 1974, with both returning results in favour of the abolition of the monarchy.
Constantine lived in exile for many decades in London, before eventually returning to his native country in 2013, where he spent the last ten years of his life.
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