Don Leoncio Alonso González de Gregorio y Álvarez de Toledo, 22nd Duke of Medina Sidonia, Grandee of Spain (born 3 January 1956) is a Spanish and historian. Born in Madrid, Medina Sidonia is the eldest son of Leoncio González de Gregorio y Martí and his wife Luisa Isabel Álvarez de Toledo, 21st Duchess of Medina Sidonia. The Duke is Professor of History at the University of Castile-La Mancha and of the Diplomatic School of the Ministry of Foreign Affairs and Cooperation.
Medina Sidonia married firstly his distant cousin María Montserrat Viñamata y Martorell, younger daughter of Luis Viñamata y Emmanueli and María de la Concepción Martorell, 23rd Countess of Alba de Liste, on 12 December 1983, and divorced in 1998. They had two children:
The Duke married secondly Pamela García Damián, of Venezuelan origin, daughter of Armando García Liceaga y Pérez de Viñaspre and María Pilar Damián Gracia, in 2001.