2017-12-05 15:36:19 UTC
King Michael ruled Romania twice, from 1927 to 1930 and then from 1940 to 1947, before the communist government ended the monarchy.
He was one of the last surviving World War Two leaders, but lived much of his life in exile.
He is best remembered for his role in making Romania change sides, from the Nazis to the Allies, in August 1944.
The death of King Michael - a cousin of Queen Elizabeth II - was announced by his family at his home on the shore of Lake Geneva on Tuesday.
He had been ill for some time and was unable to attend the funeral of his wife Queen Anne, in Romania last year.
Romania's democratic monarch
Michael was just five when he ascended to the throne for the first time in 1927. His father Carol had renounced his rights to the throne and left Romania several years earlier amid a scandal over a love affair.
His father returned in 1930, and replaced King Michael as monarch.
But King Carol II was ousted in 1940 by a military government led by the fascist Ion Antonescu and his son once again took the throne.
In 1944, the 22-year-old King Michael became involved in a coup against Antonescu and sided Romania with the Allies.
Romania's exiled King Michael, 75, tears streaming down his face, arrives together with his wife Anne in his homeland February 28, 1997
King Michael and his wife Anne during a visit to Romania in 1997
After World War Two, Michael was forced to abdicate by the country's communists, who ruled until the revolution of 1989.
The communist leaders threatened to carry out mass executions if he refused to go. In a BBC interview, he described how the authorities had blackmailed him.
"If you don't sign this thing now, we're going to have to shoot or kill 1,000 people that are already in prison."
He went into exile until the 1990s when he returned to Romania after the fall of the country's communist leader, Nicolae Ceaucescu.
The Romanian royal family settled near Geneva in Switzerland, and the former king had to find work.
He said one of his favourite jobs was as a test pilot on private aeroplanes in Europe and the United States.
In 1948, he married Anne of Bourbon-Parma, whom he had met at the wedding of the future Queen Elizabeth II and the Duke of Edinburgh in London in 1947.
King Michael's Romanian citizenship was restored in 1997.