(1 January 1861 - 20 September 1942) was a French painter born in Paris. His father was a successful psychiatrist who ran a fashionable clinic, and Blanche was brought up in the rich Parisian neighborhood of Passy in a house that had belonged to the Princesse de Lamballe. Although he received some instruction in painting from Henri Gervex, he may be regarded as self-taught. He became a very successful portrait painter, with a style derived from 18th-century English painters such as Thomas Gainsborough as well as Edouard Manet and John Singer Sargent. He worked in London, where he spent time from 1870 on, as well as Paris, where he exhibited at the Salon and the Sociate Nationale des Beaux-Arts. One of his closest friends was Marcel Proust, who helped edit several of Blanche's publications. He also knew Henry James and is mentioned in Gertrude Stein's The Autobiography of Alice B. Toklas. Among the painter's most famous works are portraits of his father, Marcel Proust (Private collection, Paris), the poet Pierre Louÿs, the Thaulow family (Musee d'Orsay, Paris), Aubrey Beardsley (National Portrait Gallery, London), and Yvette Guilbert.
He was the author of the unreliable Portraits of a Lifetime: the late Victorian era: the Edwardian pageant: 1870-1914 (London: J.M. Dent, 1937) and More Portraits of a Lifetime, 1918-1938 (London: J.M. Dent, 1939).