score:4
"Spain was a powerful kingdom ruled by Ferdinand and Isabella (or their descendants) at that time."
Charles V was one of those descendants. Specifically, his mother, Juana of Castile was the daughter of Ferdinand and Isabella, while he inherited Austria, the Holy Roman Empire, and the Netherlands from his father and the father's parents.
And Charles V controlled essentially ALL of Spain, excluding Portugal and Navarre.
Upvote:5
Easy: through his mother, who was Ferdinand and Isabella's daughter.