Younger son of Philip Le Bel of Burgundy and Juana La Loca of Spain

Ferdinand was born in Spain and raised by his grandfather and namesake, Ferdinand of Aragon.  The Spaniards would have liked the younger Ferdinand to be his grandfather's heir, rather than his elder brother, Charles V, a foreigner who did not even speak Spanish.  Why, they wondered, could Ferdinand not have Spain, and Charles the Low Countries and Austria?  However, at that time, Charles had no intention of giving up any part of his power.  As soon as he arrived in Spain, in 1517, he shipped his younger brother to the Netherlands; Ferdinand never set foot in Spain again.

Their other grandfather, Maximilian I, had arranged a double wedding between his grandchildren and the children of the king of Hungary and Bohemia.  Ferdinand married
Anna of Hungary, and his sister Mary married the future King Louis /Lajos ( pronounced 'Lay-osh') II.  Louis' death at the hands of the Turks made his brother-in-law Ferdinand king , though he insisted on being elected before accepting the double crown. 

Eventually, Charles V decided that the Habsburg inheritance would be more manageable if it was split in two.  In October 1555, he abdicated, giving Spain, the Netherlands and the Spanish possessions in Italy and the New World to his son Philip (II), while Ferdinand got the Austrian possessions and became Holy Roman Emperor.  He was supposed to leave the Imperial crown to Philip, but since that would have disinherited his own sons, he did not.

Source: Sandra White