Alexandre joined his father in New York in 1946 and became a partner in 1952. After the death of his father in 1959 in Neuilly-sur-Seine, Alexandre became the company's principal. In 1962 Alexandre was a co-founder and first President of the Art Dealers Association of America, remaining one of the association's permanent board members throughout his life. He also served as an adviser to both the American Government and the Internal Revenue Service on matters pertaining to art works. After Alexandre's premature death in 1987 in London from an aneurysm, while attending the reunion of the US Army Second Armored Division, his wife Elaine took over the business. Following the death of Micheline in 2007, the family agreed to donate their grandfather's archives to MoMA, which held a supporting exhibition of the collection in 2010.