In January 1640, 8-years-old Mary received her first marriage proposal: the 13-years-old William, the eldest son and heir of Frederick Henry, Prince of Orange, asked the hand of the princess. The mother of the potential groom, Amalia of Solms-Braunfels, was once a lady-in-waiting and close friend of Mary's aunt Elizabeth Stuart, Queen of Bohemia, which later played an important role in Mary's life. The offer of the House of Orange was at first rejected by King Charles I, who wanted to give his daughter in marriage to Balthasar Charles, Prince of Asturias, only son and heir of King Philip IV of Spain and also Mary's maternal first-cousin. A prerequisite for such a union was Mary's conversion to Catholicism, but the princess, who at the request of her mother studied the basics of the Catholic religion, did not want to change her faith. Charles I Louis, Elector Palatine, Mary's paternal first-cousin, was also a suitor for her hand, but at the end this proposal also fell through.