María del Pilar González de Gregorio y Álvarez de Toledo (born 10 January 1957), also known as Pilar Medina Sidonia, is a Spanish noblewoman, writer and socialite, who had been the former 15th Duchess of Fernandina between 1993 and 2012, until her title was revoked as a result of a legal battle with her nephew. Born in Madrid, she is the daughter of Leoncio González de Gregorio y Martí and his wife Luisa Isabel Álvarez de Toledo, 21st Duchess of Medina Sidonia. Her main seat of residence is at González de Gregorio Palace, in Quintana Redonda, Soria. Pilar is a writer, and is the author of many articles and a novel, titled Nápoles 23. Since 2011, Pilar has served as chairman of Christie's Spain.