As Philip generally told the truth to the Pope, it is probable that the secret, when once revealed, will contain the veritable solution of the mystery.  Till that moment arrives, it seems idle to attempt fathoming the matter.  Nevertheless, it may be well briefly to state the case as it stands.  As against the King, it rests upon no impregnable, but certainly upon respectable authority.  The Prince of Orange, in his famous Apology, calls Philip the murderer of his wife and of his son, and says that there was proof of the facts in France.  He alludes to the violent death of Carlos almost as if it were an indisputable truth.  “As for Don Charles,” he says, “was he not our future sovereign?  And if the father could allege against his son fit cause for death, was it not rather for us to judge him than for three or four monks or inquisitors of Spain?”

The historian, P. Matthieu, relates that Philip assembled his council of conscience; that they recommended mercy; that hereupon Philip gave the matter to the inquisition, by which tribunal Carlos was declared a heretic on account of his connexion with Protestants, and for his attempt against his father’s life was condemned to death, and that the sentence was executed by four slaves, two holding the arms, one the feet, while the fourth strangled him.

De Thou gives the following account of the transaction, having derived many of his details from the oral communications of Louis de Foix: 

Philip imagined that his son was about to escape from Spain, and to make his way to the Netherlands.  The King also believed himself in danger of assassination from Carlos, his chief evidence being that the Prince always carried pistols in the pockets of his loose breeches.  As Carlos wished always to be alone at night without any domestic in his chamber, de Foix had arranged for him a set of pulleys, by means of which he could open or shut his door without rising from his bed.  He always slept with two pistols and two drawn swords under his pillow, and had two loaded arquebusses in a wardrobe close at hand.  These remarkable precautions would seem rather to indicate a profound fear of being himself assassinated; but they were nevertheless supposed to justify Philip’s suspicions, that the Infante was meditating parricide.  On Christmas eve, however (1567), Don Carlos told his confessor that he had determined to kill a man.  The priest, in consequence, refused to admit him to the communion.  The Prince demanded, at least, a wafer which was not consecrated, in order that he might seem to the people to be participating in the sacrament.  The confessor declined the proposal, and immediately repairing to the King, narrated the whole story.  Philip exclaimed that he was himself the man whom the Prince intended to kill, but that measures should be forthwith taken to prevent such a design.  The monarch then consulted the Holy Office of the inquisition, and the resolution was taken to arrest his son.  De Foix was compelled