While still only 15 years old Philip II of Spain accompanied the Duke of Alba in the siege of Perpignan, in August 1542. So, suppose the young prince is wounded or get a disease and dies in late August or early September 1542. It wouldn't change the outcome of the 9th Italian War between the Habsburgs and the Valois. But what would happen then?
Charles V never remarried IOTL after the death of his wife Isabella of Portugal. Would he make his daughter Mary his heir? She would probably still be married to a son of Ferdinand I, if not Maximilian as IOTL, and so the Spanish inheritance would be kept with the Habsburgs. Or would Charles search for a bride in order to try to have a male heir? And if he does so, who could be his new wife?
Charles V never remarried IOTL after the death of his wife Isabella of Portugal. Would he make his daughter Mary his heir? She would probably still be married to a son of Ferdinand I, if not Maximilian as IOTL, and so the Spanish inheritance would be kept with the Habsburgs. Or would Charles search for a bride in order to try to have a male heir? And if he does so, who could be his new wife?