Leoncio Alonso González de Gregorio y Álvarez de Toledo, 22nd Duke of Medina Sidonia, GE (born 3 January 1956) is a Spanish aristocrat 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.

González de Gregorio married firstly his distant cousin María Montserrat Viñamata y Martorell, younger daughter of Luis Viñamata y Emmanueli and The 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.