Madame Royale (French pronunciation: ​[madam ʁwajal], Royal Lady) was a style customarily used for the eldest living unmarried daughter of a reigning French monarch. It was similar to the style Monsieur, which was typically used by the King's second son. Just as Gaston, duc d'Orléans (1608–1660), the second son of King Henry IV of France (1553–1610), was known as Monsieur, Elisabeth of Bourbon (1602–1644), the eldest daughter of Henry, was known before her marriage to King Philip IV of Spain (1605–1665) as Madame Royale. After her death, the title was borne by her younger sister, Christine Marie of France (1606–1663), until her marriage to Victor Amadeus I, Duke of Savoy (1587–1637).