A statement by Hygeia Hospital said the former king suffered a stroke and complications from other health problems.

He was the last ruler in a 19th-century family dynasty whose connections to Greece were tenuous but that sought to draw legitimacy from connections to the wider family tree of European royalty.

He lived for decades in London and was a cousin of King Charles III, a godfather to Prince William and part of the family line of Greece-born Prince Philip. The former king traveled as Constantine de Grecia under a Danish passport as a result of his family’s shared lineage with a branch of Denmark’s royal family — in addition to his marriage to a former Danish princess, Ann-Marie. His sister Sophia is the wife of the former Spanish king Juan Carlos.

But for Greeks, he remained deeply woven into the history of the 1967-1974 right-wing dictatorship, whose ruthless suppression of opposition still resonates as uncomfortable memories in the country’s political and cultural life.

Events began to unfold in 1965 when the young king feuded with Prime Minister Georgios Papandreou, leading to the collapse of his government. The political crisis — still known in Greece as the “Apostasy” — began a period of upheavals and caretaker governments.

“The people don’t want you, take your mother and go!” protesters shouted in 1965 in denunciations of the king and his mother, Queen Frederica.

The ongoing political unrest was used by a clique of Greek military officers as justification to take control of the country in April 1967. The “colonels,” as they were known, also feared that the king was planning preemptive moves to install his backers in power.

Backed into a corner, he agreed to officially inaugurate the junta as Greece’s new leaders. The king and his family then relocated to northern Greece, seeking to lead a countercoup. The plans fell apart and the family fled to Rome and later settled in London.

Stylianos Pattakos, last surviving member of Greek junta ‘colonels,’ dies at 103

“It was the worst day of my life,” he said in describing the departure from Greece in a 2015 memoir released by the Greek newspaper To Vima. “That day, I saw my first white hair.”

Some officers in the Greek navy remained loyal to him and, in 1973, made another attempt at a revolt against the junta. The military rulers abolished the monarchy — even as he continued to claim he was Greece’s rightful monarch.

Junta leader George Papadopoulos labeled the former king “a collaborator with foreign forces and with murderers.”

After the dictatorship collapsed in 1974 — following a military crisis with Turkey over Greek attempts to unite with the island nation of Cyprus — he sought to make a dramatic return. He was advised to wait by political leaders, who were worried he would upset efforts to restore democracy. Instead, a referendum was held on whether to bring back the monarchy.

On the eve of the vote, the former king seemed confident. The outcome “will find my family and me back home,” he said from London. Yet nearly 70 percent of the votes cast were against reestablishing the royal family. The prime minister, Constantine Karamanlis, was quoted as saying that the voters had rid the nation of a cancerous growth.

The former king did not return to Greece until 1981, after being given clearance for a five-hour visit to bury his mother in the family cemetery of the former royal palace at Tatoi, north of Athens. (The Greek government announced that the former king’s remains would also be interred there.)

From London, the former king used his royal title and claimed ownership of family land in Greece, including Tatoi. In 1994, the Greek government formally stripped him of his citizenship and confiscated the royal property.

A lawsuit he filed in the European Court of Human Rights resulted in a 12 million euro award — far less than the 500 million euros he sought. In 1995, he boasted to Vanity Fair that he received 65,000 letters a year from Greek citizens and needed a four-person staff to help handle his affairs.

His life in exile was far from a bumpy ride. He hobnobbed with other members of European royalty, who often called him “Your Majesty.” He and his wife lived in a manse in London’s tony Hampstead Garden Suburb. If the British royals threw a gala, he was on the guest list.

When Athens hosted the Olympics in 2004, he returned as an honorary member of the International Olympic Committee. The appearance, however, was intentionally subdued at the request of organizers despite his stature as a past Olympic medal winner.

At the 1960 Rome Games, the then crown prince was part of the gold medal-winning team in three-person Dragon Class sailing. He also was the flag-bearer at the Rome Opening Ceremonies, and a Greek postage stamp was made in honor of his team’s victory.

In an interview with NBC’s “Today” during the Athens Olympics, the former king called Greece “his country.”

“I remember I had the privilege of holding the flag when our team came in,” he said, recounting the Rome Games, “and the roar of the crowd was something that is still in my ears.”

For more than a decade, he spent increasing time in Greece as authorities made accommodations and as protests over his presence largely faded. He also made some slight concessions. He belatedly recognized that the age of the monarchy in Greece was long over.

His official website listed him as King Constantine, former King of the Hellenes.

The future king was born on June 2, 1940, in Athens to Princess Frederica of Hanover and Prince Paul, the younger brother of Greece’s King George II and heir to the throne.

Before Prince Constantine’s first birthday, the family fled for Alexandria, Egypt, as Nazi forces occupied much of the country. The family later spent time in South Africa before returning to Greece in 1946 — just as the country was moving into a disastrous civil war between communist-backed forces and nationalists, many loyal to the monarchy.

The nationalist side won, but political rifts remained strong for decades and spilled over into divided views on the monarchy — which some critics decried as outsiders with family links to wartime foe Germany.

The prince was educated at boarding schools and military academies in preparation for the throne. His turn came in 1964, when was he was 23, after the death of his father, King Paul. (The family had ruled Greece since 1863 except for 1924 to 1935).

The final king of Greece is survived by Anne-Marie, his wife of 58 years; five children, Alexia, Pavlos, Nikolaos, Theodora and Philippos; and nine grandchildren.

His lineage tracks back to the House of Schleswig-Holstein-Sonderburg-Glücksburg, which includes Denmark and other countries. He refused to adopt any of those names, however, after the Greek government said he could have his passport restored only if he adopted a surname.

“I don’t have a name,” he said in 1995 in London. “My family doesn’t have a name.”

Glücksburg is the name of a place, he noted, like any London borough.

“I may as well call myself Mr. Kensington,” he said.