Don Agustín Fernando Muñoz y Sánchez, 1st Duke of Riánsares, 1st Marquess of San Agustín, 1st Duke de Montmorot, was the second and morganatic husband of Maria Christina, Regent of Spain.

Maria Christina of the Two Sicilies was the queen consort of Spain from 1829 to 1833 and queen regent of the kingdom from 1833, when her daughter became queen at age two, to 1840. By virtue of her short marriage to King Ferdinand VII of Spain, she became a central character in Spanish history for nearly 50 years, thanks to introducing a bicameral model of government based on the Bourbon Restoration in France: the Spanish Royal Statute of 1834.