Son of Philip III of Spain and Margarethe of Austria.  As a younger son, he was destined by his parents for the church, although he had no vocation, and made a Cardinal in his childhood.  When he was appointed to the goverorship of the Netherlands in 1634, Archduchess Isabella pointed out that the Fllemings disliked the idea of Cardinals as rulers, and suggested that they would find it easier to accept Ferdinand if he didn't wear his vestments.  Nothing could have suited him better; after that, all his portraits show him  either in armour or in military uniform!

Source: Sandra White