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