By Charles V I mean King of Spain and Holy Roman Emperor, oldest son of Joanna the Mad and Philip Habsburg. Assuming (let's be butterfly killer for a moment) rest of Juana's issue is more or less OTL, what would be effects of such change? Ferdinand (born in Spain as future heir of Castile and Aragon, thus IMHO still given Spanish name) is thus only male heir of Philip and Joanna. Is he still raised in Spain? Having Spanish born heir Spain is going to avoid Comuneros revolt, OTOH being only living male Habsburg after death of grandfather Ferdinand is going to face more troubles managing whole Habsburg inheritance. Perhaps, with future of Habsburg dynasty less secure than IOTL, HRE Max is going to marry for fourth time? What is going to happen with Ferdinand's five sisters ITTL?