
Philip IV of Spain
Balthasar Carlos was born in 1629 to Philip IV of Spain and his French wife Elisabeth. Elisabeth produced seven children but only two, Balthasar and his sister Maria Theresa, survived. Balthasar was a robust and healthy child. On October 5, 1646, Balthasar fell ill. He was diagnosed with smallpox and many feared he would die. However, Balthasar recovered.
In 1644, Elisabeth of France, Queen Consort of Spain, died. Philip IV sought a remarriage and negotiated the hand of the French princess Anna Marie Louise d'Orleans, also known as La Grande Madmoiselle. In 1648, she was married by proxy in France. She then went to Spain and met her husband.
Balthasar Carlos, Prince of Asturias, was married in 1647 to his cousin Archduchess Mariana of Austria. In 1649, Mariana gave birth to a son, Philip. In 1650, Mariana had a daughter, Maria Ambrosia. Both Philip and Maria Ambrosia died in infancy. In 1654, Mariana had a son, Carlos Balthasar Jose and in 1656, a healthy daughter, Margaret Theresa.
Philip IV had a spare heir in 1652 when La Grande Madmoiselle gave birth to a son, Prince Philip.
Philip IV's eldest daughter, the Infanta Maria Theresa, was married in 1659 to Louis XIV of France as part of the Treaty of the Pyrenees. The treaty came with a clause that Maria Theresa would renounce all claims to Spain for herself and her descendants. However, Maria's dowry was never claimed so Louis XIV claimed rights to the Spanish throne. Maria Theresa quickly produced an heir, Louis le Grand Dauphin.
In 1658, Holy Roman Emperor Ferdinand III died, leaving his son Archduke Leopold as Holy Roman Emperor Leopold I. Leopold married Marguerite Louise of France, who was coincidentally sister to La Grande Madmoiselle. Marguerite Louise suffered three miscarriages before giving birth to a son, Charles. However, she died of complications. Leopold remarried to Louise Marie of the Palatinate, who provided a spare heir, Joseph, and a daughter Maria.
Philip IV of Spain died in 1667* and Balthasar Carlos became Carlos II of Spain. Philip IV was mourned by few. he had brought Spain to bankruptcy with his pointless war with the Portugese. Carlos II had not a penny in his pocket.
*Due to butterflies, he dies two years later than IOTL.