Original: However, other Protestants supported the stance taken by the Catholics, and in 1617, Ferdinand was duly elected by the Bohemian estates to become the Crown Prince, and automatically upon the death of Matthias, the next King of Bohemia.
Simplified: So, in 1617, Ferdinand was elected by the Bohemian Estates to become the Crown Prince, and automatically upon the death of Matthias, the next King of Bohemia.