So, this is something that's become a bit of a favourite of mine. In otl, Holy Roman Emperor Ferdinand had three sons who lived past infancy, Ferdinand IV, Leopold I and Charles Joseph. Ferdinand IV died in 1654, Leopold eventually took on the purple, and Charles died in 1664 aged fifteen. My question is this, if Charles Joseph does not die in 1664, what role might he play in Habsburg politics? Would he be made Archduke of Inner or Further Austria, or perhaps even Tyrol? Whom might he marry, Bourbon? A German princess? Would he play a role in the military affairs of his brother, and perhaps develop a reputation as a soldier and commander? Working alongside Prince Eugene of Savoy.