Which Spanish prince commanded at the Battle of Nördlingen?

The Spanish prince who commanded at the Battle of Nördlingen was Cardinal-Infante Ferdinand. The battle, fought on 5–6 September 1634, ended in a decisive Imperial-Spanish victory over the Swedish-German army.

Ferdinand was the younger brother of Philip IV of Spain and had been appointed governor of the Spanish Netherlands. While travelling there with a Spanish army, he joined forces with his cousin, Ferdinand of Hungary, near Nördlingen. Together they confronted Swedish commanders Gustav Horn and Bernhard of Saxe-Weimar, who were attempting to relieve the besieged town.

The Spanish infantry, especially its veteran tercios, played a major role in repelling repeated Swedish assaults. The defeat shattered Swedish influence in southern Germany and helped prompt France to enter the war directly against the Habsburgs. Ferdinand of Hungary was also an important commander, but the question asks for the Spanish prince specifically. The other options are misleading: Philip IV was king rather than battlefield commander, while the Duke of Olivares was a powerful minister and Don Juan of Austria belonged to a different generation.