Monsieur Gaston, Duke of Orléans (Gaston Jean Baptiste; 24 April 1608 – 2 February 1660), was the third son of King Henry IV of France and his second wife, Marie de' Medici. As a son of the king, he was born a Fils de France. He later acquired the title Duke of Orléans, by which he was generally known during his adulthood. As the eldest surviving brother of King Louis XIII, he was known at court by the traditional honorific Monsieur.