A son of a Spanish or Portuguese master apart from the heir into throne.
Any child of the master of Spain or Portugal, except the oldest or heir obvious.
A title directed at all of sons of the kings of Spain and Portugal, except the eldest or heir evident.
A son of a Spanish or Portuguese sovereign; in particular usage as a title, a younger prince of the royal blood. The oldest son or heir evident in Spain is named Prince of Asturias, while the heir evident of Portugal ended up being known as Prince of Brazil until that nation became independent.