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 to alter the pulleys of the door to the Prince’s chamber in such a manner that it could be opened without the usual noise, which was almost sure to awaken him.  At midnight, accordingly, Count Lerma entered the room so stealthily that the arms were all, removed from the Prince’s pillow and the wardrobe, without awakening the sleeper.  Philip, Ruy Gomez, the Duke de Feria, and two other nobles, then noiselessly, crept into the apartment.  Carlos still slept so profoundly that it was necessary for Derma to shake him violently by the arm before he could be aroused.  Starting from his sleep in the dead of night, and seeing his father thus accompanied, before his bed, the Prince cried out that he was a dead man, and earnestly besought the bystanders to make an end of him at once.  Philip assured him, however, that he was not come to kill him, but to chastise him paternally, and to recal him to his duty.  He then read him a serious lecture, caused him to rise from his bed, took away his servants, and placed him under guard.  He was made to array himself in mourning habiliments, and to sleep on a truckle bed.  The Prince was in despair.  He soon made various attempts upon his own life.  He threw himself into the fire, but was rescued by his guards, with his clothes all in flames.  He passed several days without taking