William Mostyn-Owen

William "Willy" Mostyn-Owen (10 May 1929 – 2 May 2011) was a British art historian. He worked for some years with the art expert Bernard Berenson, and was his bibliographer, and later for the auctioneers Christie's.

William Mostyn-Owen was born on 10 May 1929 into a military family, the son of Lt-Col Roger Arthur Mostyn-Owen (1888–1947) and Margaret Eva Dewhurst. He had three older brothers and a sister. His brothers all died during the Second World War, and his father died while William was in his teens, so that he inherited the family seat of Woodhouse, Shropshire, and Aberuchill Castle, Perthshire, at a young age. He was educated at Eton and Magdalene College, Cambridge.

After graduation, Mostyn-Owen worked for the Fogg Museum at Harvard and the Metropolitan Museum in New York. In the 1950s, he spent six years working closely with Bernard Berenson, the art expert, at his Villa I Tatti near Florence, and acquired a deep understanding of the art of the Italian Renaissance. In Florence, the British consul noted that Mostyn-Owen was "worth a battleship" for his charm and tact when dealing with American President Harry Truman, the King of Norway and other visiting notables.

He joined the auction house Christie's in London, alongside David Carritt, Noel Annesley, and Brian Sewell, and worked there for almost thirty years. He became a director in 1968, and chairman of Christie's Education from 1979 to 1988.

Mostyn-Owen's first wife was the Italian writer Gaia Servadio, with whom he had three children, Owen, Allegra and Orlando. In 1968, they were living in a single wing of Aberuchill Castle which consisted of "23 rooms or so". His second wife was Faith Clark, and his third was Jane Martineau, also an art historian, whom he married in 1992. His daughter Allegra was the first wife of the politician Boris Johnson.