Balthasar Carlos survives
The survival of the Prince
His father soon began diplomatic efforts to seek a bride: Archduchess Mariana of Austria, daughter of Holy Roman Emperor Ferdinand III and his paternal aunt, Maria Anna, and therefore his cousin, being chosen. Another cousin, the daughter of his mother's sister, Henrietta Maria and her husband, King Charles I of England, Mary, Princess Royal, was also proposed as a potential bride - but was turned down on grounds of religion.
After the Catalan revolt of 1640, Philip IV tried to win over Aragon to raise money and men for the new war front. One of the steps taken towards this end was to bring the Prince Balthasar Charles to be sworn as crown prince of the Kingdom of Aragón. The oath was held on 20 August 1645, when the prince was sixteen years old, in the Cathedral of the Savior, Zaragoza. This titled him as Prince of Gerona, Governor General of Aragon, Duke of Montblanc, Count of Cervera and Lord of the City of Balaguer. Meanwhile, on 13 November of that year, Balthasar Charles was also sworn as heir to the Kingdom of Valencia, on 1662, Philip IV would die and Balthasar Carlos would reign as Charles II.
On February 2, 1645, Archduchess Mariana of Austria would marry Balthasar Charles of Austria.
The marriage of Mariana of Austria and Balthasar Charles would produce the following children: Margaret Therese b. 1647, Philip Propsero b. 1658 d. 1661 and Charles b. 1661.