So, let's assume that Philip II of Spain and Mary I of England have two children, a daughter named Catherine and a son named Philip born in 1555 and 1556 respectively.
Let's then say that Don Carlos, Philip II's first born son dies as otl in 1568, Philip's son by Mary is now heir apparent to the Spanish throne.
What happens next? Does Philip look to remarry, should Mary die, and try to name his son or child by his third wife his new heir in Spain?
If not, how do England and Spain handle the potential for a personal union?
Let's then say that Don Carlos, Philip II's first born son dies as otl in 1568, Philip's son by Mary is now heir apparent to the Spanish throne.
What happens next? Does Philip look to remarry, should Mary die, and try to name his son or child by his third wife his new heir in Spain?
If not, how do England and Spain handle the potential for a personal union?