The names of Philip IV's children run as:
Francis Ferdinand
Charles
John
Balthasar Charles
Philip Prospero
Ferdinand Thomas Charles
Main differences will be no OTL Charles II of Spain, means no War of the Spanish Succession, meaning the Spanish Empire (Southern Netherlands and Spain's overseas empire, stretching from the Americas to the Spanish East Indies.)
So the name is most likely going to be:
Ferdinand Charles, Prince of Asturias born 14 August 1621, and he would most likely be able to live out at least 60 years (unless he is involved in a war), so around 1681, would be his date of death.
IOTL Philip IV, began diplomatic efforts to seek a bride for Balthasar Charles, Prince of Asturias.
- First suggestion was Archduchess Mariana of Austria, daughter of Holy Roman Emperor Ferdinand III and his paternal aunt, Maria Anna, and therefore his cousin, being chosen, IOTL she would marry her uncle King Philip IV.
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
Other brides are:
- Anna de' Medici (1616-1676) daughter of Cosimo II de' Medici, and Maria Maddalena of Austria, a daughter of Charles II, Archduke of Austria, and a sister of Emperor Ferdinand II. IOTL she married Ferdinand Charles, Archduke of Austria (1628–1662) and had issue.
- Princess Luisa Cristina of Savoy, daughter of ctor Amadeus I, Duke of Savoy and Christine Marie of France
-Anna Catherine Constance Vasa, Polish princess as daughter of King Sigismund III Vasa of Poland
- Anne Marie Louise d'Orléans, Duchess of Montpensier, daugher of Gaston d'Orléans, and his first wife Marie de Bourbon, Duchess of Montpensier, had a string of proposals from various members of European ruling families, including Charles II of England, Afonso VI of Portugal, and Charles Emmanuel II of Savoy.
- Anna Beatrice d'Este (1626–1690), daugher of Alfonso III d'Este, Duke of Modena and Isabella of Savoy
- Princess Louise of Savoy, daughter of Thomas Francis, Prince of Carignano and Marie de Bourbon