It depends on the kind of inheritance.
If you have absolute agnatic inheritance, every man in the kingdom has a claim to the throne before Cass, if they have agnatic-cognatic inheritance, which is more likely, there's the question of generational back inheritance, which usually doesn't happen unless the entire patrilinear branch of the family is pruned.
Agnatic-cognatic inheritance is usually the rule, which means unless there are no children of the king left, the kings brothers get the land. At that point inheritance is again decided by primogeniture (first come first served).