Curtis Roosevelt, who lived in the White House as a child when his grandfather was US president and worked for two decades at the United Nations, has died aged 86.
The oldest grandchild of Franklin D. and Eleanor Roosevelt died of a heart attack in Saint-Bonnet-du-Gard in southern France on September 26.
Curtis Roosevelt insisted before his death that he did not want a funeral service. Instead, according to his widow Marina Roosevelt, he said: "If you must do something, then get together and have a good time, with wine and cheese, and make awful martinis like my grandfather did."
Roosevelt's childhood in the spotlight marked the rest of his life, as did his grandfather's exceptional legacy.
Curtis Roosevelt, born April 19 1930 when his grandfather was governor of New York, was the son of Anna Roosevelt, the president's eldest child and only daughter.
Curtis and his sister Anna moved in with their grandparents as his father Curtis Bean Dall's stock market career suffered in the Depression and his parents divorced.
Dubbed Buzzie and Sistie, they lived relatively shielded from the difficulty of the era, shuttling between Washington and holidays at the Roosevelt family estate in Hyde Park, New York.
The children lived in the White House for several years until their mother married a newspaper reporter John Boettiger.
"He never really got over those early impressions," his sister Anna Eleanor Seagraves said on Saturday from her home in Bethesda, Maryland, in the US.
Curtis Roosevelt went on to work as an educator and political reformer in New York, and then became a diplomat at the UN from 1964 to 1983, where he notably served as liaison with non-governmental organisations.
He was following in the footsteps of his grandmother, Eleanor Roosevelt, who was a member of the first American delegation to the UN in 1945, and later served as chairman of the UN Commission on Human Rights from 1947 to 1951.
In his memoirs, Curtis Roosevelt had both praise and criticism for his grandparents, seeing them as more engrossed in world politics than family matters.
But they always loomed large for him, Marina Roosevelt said from their home in Saint-Bonnet-du-Gard.
Roosevelt defended his grandfather's efforts to hide his polio-stricken legs from the American public.
"FDR was a Victorian," Roosevelt wrote. "You do not display your illness, and if somebody asks you how you are, you say, 'Fine.' Besides, he wanted a practical way to carry on with what he had to do and who he was."
In 2005, Curtis Roosevelt joined the grandsons of Soviet leader Josef Stalin and wartime leader Sir Winston Churchill in a debate over the legacy of their grandfathers' historic summit at Yalta 60 years earlier, which laid the groundwork for the post-war division of Europe and the Cold War.
"Nobody got what they wanted from Yalta except the Russians, who were in a position to get it," Curtis Roosevelt said at the meeting at the University of Maastricht in the Netherlands.
He said that for his grandfather, the decisions made at Yalta were mostly about accepting reality after the United States' late entry into the war.
The Yalta conference took place as Stalin's army was poised for the final attack on Berlin after occupying Poland. Stalin had the largest army in Europe, with 12 million soldiers, while Eisenhower's four million men were still west of the Rhine.
Roosevelt's fourth marriage proved the most lasting. His widow Marina hopes to fulfil his wishes for an informal memorial gathering in late November.
Curtis Roosevelt is survived by his widow, sister, daughter Julianna Roosevelt and half-brother John Boettiger of California, and a grandson.