Antoine Bibesco or, in Romanian, Anton Bibescu (July 19, 1878 - September 2, 1951) was a Romanian prince, born into an old boyer family, descended from the House of Caput who, in the words of Marcel Proust, could "legitimately claim to stand in the line of succession to the throne of France". He was a barrister, a diplomat and a writer.

As a young man his mother's celebrated Paris salon gave him the opportunity to meet (among many other notables) Charles Gounod, Claude Debussy, Camille Saint-Saëns, Pierre Bonnard, Édouard Vuillard, Aristide Maillol, and Anatole France and Marcel Proust.

Proust became a lifelong friend and shared a secret language in which Marcel was "Lecram" and the Bibescos were "Ocsebib". Antoine made every effort to have "Du Cote de Chez Swann" published by André Gide and the Nouvelle Revue Francaise but failed in his efforts. Toward the end of Proust's life, Bibesco, who was a great raconteur, played the role of an outside ear for the reclusive writer. Later he published "Letters of Marcel Proust to Antoine Bibesco".

Before World War I Prince Antoine was a Romanian envoy in London and by 1918 had entered the Asquith (former Liberal Prime Minister) circle. At this time he was in a relationship with the writer Enid Bagnold but his affections for her were replaced by those he began to feel for the twenty-one-year-old Elizabeth Asquith (he was 40 at the time). Margot Asquith, her mother, thought he would be a steadying influence on her daughter. "What a gentleman he is. None of my family are gentlemen like that; no breeding you know." The marriage took place at St. Margaret's, Westminster on April 29, 1919. It was the society event of the year.

Antoine continued his diplomatic career in Washington (1920-1926) and Madrid (1927-1931). The Second World War years were spent in Romania where his wife died (in 1945) and when his estates were confiscated by the communists he left that country, never to return. Enid Bagnold, in her autobiography, tells of smuggling silver across the English channel for him. He died on September 2, 1951.

"He had three tombs in his heart," Enid Bagnold wrote in her Times obituary, "which I think he could never finally close - of his mother, his brother Emmanuel and his wife."