After the marriage of her older sister Elisabeth in 1615 to the future Philip IV of Spain , Christine took on the honorary title of Madame Royale indicating her status as the eldest and most senior unmarried daughter at the court of her father .
After the marriage of Princess Élisabeth in 1615 to the future Philip IV of Spain , Christine took on the honorary title of Madame Royale indicating her status as the eldest and most senior unmarried daughter at the court .