Rollerblading near his summer home in the fashionable resort of Southampton, Long Island, he seems to have fallen into the path of a passing car, perhaps absorbed by the music on his Walkman.
Duke was one of the great American heirs. He inherited a substantial fortune from his great-uncle, James Buchanan ''Buck'' Duke, founder of the American Tobacco Company and of the university in North Carolina which bears his name. He was a cousin of Doris Duke, whose death 18 months ago is being investigated to see whether she was murdered.
On the other side of his family he was descended from the great Philadelphia clan of the Biddles, whose wealth goes back to 18th-century wine-merchants. A tall, impeccably tailored figure, Duke moved naturally into the diplomatic world and served as ambassador to El Salvador, Denmark, Spain and Morocco. He is said to have managed relations between the United States and the Franco regime in Madrid with considerable tact.
He was chef de protocol at the Department of State in Washington under Presidents Kennedy and Johnson. If, as has been said, the essential difference between the Kennedy administration and the Eisenhower administration which succeeded it was that elderly millionaires in brown suits who played golf were replaced by youthful millionaires in blue suits who played tennis, Duke was in his element in Kennedy Washington.
Perhaps his finest hour as the professional diplomat came when it fell to him to organise the festivities attending Kennedy's funeral. As a young man he was a Republican, as befitted his caste and at least the Philadelphian side of his lineage. But he converted to the Democrats, and served for a time for $1 a year as New York City's Commissioner of Civic Affairs and Public Events.
Angier Biddle Duke, diplomat: born New York 30 November 1915; four times married (three sons, one daughter); died Southampton, Long Island 29 April 1995.