Here we're talking about Philip II of Spain's son with his first wife and double first cousin Maria Manuela of Portugal. IOTL Carlos was meant to marry Elisabeth, daughter of Henri II of France and Catherine de Medici', but died before the wedding could go through. Philip himself would marry Elisabeth, and had two surviving daughters with her.
So, to introduce a relatively complex scenario: Let's say Carlos lives longer to marry Elisabeth, have a daughter with her, and still predecease his father. What would the dynamic be ITTL? Assuming Philip's marriage to Mary Tudor produces no issue as IOTL, does he still remarry, given that he has a granddaughter but no surviving sons or grandsons? Would said daughter inherit something of the Spanish realms?
So, to introduce a relatively complex scenario: Let's say Carlos lives longer to marry Elisabeth, have a daughter with her, and still predecease his father. What would the dynamic be ITTL? Assuming Philip's marriage to Mary Tudor produces no issue as IOTL, does he still remarry, given that he has a granddaughter but no surviving sons or grandsons? Would said daughter inherit something of the Spanish realms?