He was excessively angry at the suggestion that the prince who was expected to spring from his father’s marriage with the English queen, would one day reign over the Netherlands, and swore he would challenge him to mortal combat in order to prevent such an infringement of his rights.  His father and grandfather were both highly diverted with this manifestation of spirit, but it was not decreed that the world should witness the execution of these fraternal intentions against the babe which was never to be born.

Ferocity, in short, seems to have been the leading characteristic of the unhappy Carlos.  His preceptor, a man of learning and merit, who was called “the honorable John”, tried to mitigate this excessive ardor of temperament by a course of Cicero de Officiis, which he read to him daily.  Neither the eloquence of Tully, however, nor the precepts of the honorable John made the least impression upon this very savage nature.  As he grew older he did not grow wiser nor more gentle.  He was prematurely and grossly licentious.  All the money which as a boy, he was allowed, he spent upon women of low character, and when he was penniless, he gave them his chains, his medals, even the clothes from his back.  He took pleasure in affronting respectable females when he met them in the streets, insulting them by the coarsest language and gestures.  Being cruel, cunning, fierce and licentious, he seemed to combine many of the worst qualities of a lunatic.  That he probably was one is the best defence which can be offered for his conduct.  In attempting to offer violence to a female, while he was at the university of Alcala, he fell down a stone staircase, from which cause he was laid up for a long time with a severely wounded head, and was supposed to have injured his brain.

The traits of ferocity recorded of him during his short life are so numerous that humanity can hardly desire that it should have been prolonged.  A few drops of water having once fallen upon his head from a window, as he passed through the street, he gave peremptory orders to his guard to burn the house to the ground, and to put every one of its inhabitants to the sword.  The soldiers went forthwith to execute the order, but more humane than their master, returned with the excuse that the Holy Sacrament of the Viaticum had that moment been carried into the house.  This appeal to the superstition of the Prince successfully suspended the execution of the crimes which his inconceivable malignity had contemplated.  On another occasion, a nobleman, who slept near his chamber, failed to answer his bell on the instant.  Springing upon his dilatory attendant, as soon as he made his appearance, the Prince seized him in his arms and was about to throw him from the window, when the cries of the unfortunate chamberlain attracted attention, and procured a rescue.

The Cardinal Espinoza had once accidentally detained at his palace an actor who was to perform a favorite part by express command of Don Carlos.  Furious at this detention, the Prince took the priest by the throat as soon as he presented himself at the palace, and plucking his dagger from its sheath, swore, by the soul of his father, that he would take his life on the spot.  The grand inquisitor fell on his knees and begged for mercy, but it is probable that the entrance of the King alone saved his life.