The ordinance concerning the imprisonment of Don Carlos was so strictly observed, that the queen and the princess Jane, who wished to see and console him, were refused permission to do so by the king. Philip was so suspicious of every one, that he lived in a kind of captivity, and did not make his accustomed excursions to Aranjuez, the Pardo, and the Escurial. He kept himself shut up in his apartment; the least noise in the street drew him to the window, such was his dread of some tumult. He had always suspected the Flemings, or other persons, of being the prince's partisans, or at least to affect it.

The unhappy Don Carlos, who was not accustomed to conquer his passions, could never make use of any means to palliate his misfortune. He gave himself up to the greatest impatience, and refused to confess, to enable himself to fulfil the duty always performed by the royal family on Palm Sunday. His old master, the Bishop of Osma, had died in 1566. The king commanded the Doctor Suarez de Toledo, his first almoner, to visit him, and try to persuade him: his efforts were unavailing, though Don Carlos always treated him with great respect. On Easter-day, Suarez wrote a long and touching letter to him, in which he proved by unanswerable arguments, that his highness did not take the proper means of terminating the affair favourably. He represented that his highness had no longer either friends or partisans, and reminded him of several scandalous scenes which had increased the number of his enemies; he finishes his letter in the following terms: "Your highness may easily imagine all that will be said when it is known that you do not confess, and when many other terrible things are discovered; some are so much so, that if it concerned any other person than your highness, the holy office would be entitled to inquire if you are really a Christian. I declare to your highness, with all truth and fidelity, that you only expose yourself to lose your rank, and (what is worse) your soul. I am obliged to say, in the grief and bitterness of my heart, that there is no remedy, and the only advice I can give you, is to return towards God and your father, who is his representative on earth. If your highness will follow my advice, you will apply to the president, and other virtuous persons, who will not fail to tell you the truth, and conduct you in the right way." This letter had no more success than any of the other attempts; the prince still refused to confess.

The despair which Don Carlos soon felt, made him neglect all regularity in taking food and rest. He became so heated by the rage which preyed on him, that iced water (which he used continually) had no effect on him. He caused a great quantity of ice to be put into his bed, to temper the dryness of his skin, which was become insupportable. He walked about naked, and without shoes or stockings, on the pavement, and remained whole nights in this state. In the month of June, he refused all nourishment but iced water, for eleven days, and became so weak that it was supposed he had not long to live. The king being informed, went to visit him, and addressed some words of consolation to him, the result of which was to induce the prince to eat more than was proper for him in his weak state, and this excess brought on a malignant fever, accompanied by a dangerous dysentery. The prince was attended by Doctor Olivares, chief physician to the king; he went in alone to the patient, and when he returned, held a consultation with the other physicians of the king, in the presence of the Prince d'Evoli.

The preliminary case, drawn by Don Diego Bribiesca de Muñatones, was sufficiently advanced in the month of July, to allow of a final sentence, without examining the criminal, or to appoint a procurator for the king, who in quality of fiscal accused the prince of the crimes stated in the preparatory instruction. No judicial notice was sent to the prince; they had only the declarations of the witnesses, letters, and other papers.

These writings proved that, according to the laws of the kingdom, Don Carlos must be condemned to death, for high treason, on two counts: first, for having attempted parricide; and secondly, for having framed a plan to usurp the sovereignty of Flanders, by means of a civil war. Muñatones made a report of this, and the punishments established for such crimes, to the king; he added, that particular circumstances, and the rank of the criminal, might authorize his majesty to declare, that general laws could not affect the eldest sons of kings, because they were subject to laws of a higher nature, those which related to policy, and the welfare of the state; lastly, that the monarch might, for the good of his subjects, commute the punishment.

Cardinal Espinosa and the Prince of Evoli were of the opinion of Muñatones; Philip then said, that his heart inclined him to follow their advice, but that his conscience would not permit him to do so: that he thought it would be far from being a benefit to Spain; that, on the contrary, he thought it would be the greatest misfortune that could happen to his kingdom, to be governed by a king devoid of knowledge, talents, judgment, or virtue, full of vices and passions, and, above all, furious, ferocious and sanguinary; that these considerations compelled him, notwithstanding his attachment to his son, and his anguish at so terrible a sacrifice, to suffer the laws to take their course; but considering that the health of Don Carlos was in such a state that there was no hope of prolonging his life, he thought it would be better to suffer him to satisfy himself in his inclinations in eating and drinking, since, from the disorder of his ideas, he would not fail to commit some excess, which would lead him to the tomb: that the only thing which concerned him, was the necessity of persuading his son that his death was inevitable, and that in consequence he must confess himself to ensure salvation; that this was the greatest proof of affection which he could show to his son and the Spanish nation.

This decision of the king is not mentioned in the writings of the trial. There was no sentence written or signed; but the secretary Hoyo, in a note, says, that at this period of the trial the prince died of his malady, and this was the reason why no sentence was pronounced. The proof of the fact exists in other papers, in which the curious anecdotes of the time have been related. Although these documents are not authentic, they merit attention, as they were written by persons employed in the king's palace, and accord with what some writers have insinuated. It is true that they did think proper not to speak plainly on such delicate subjects, but they have said enough to lead to the truth.

Cardinal Espinosa and the Prince of Evoli thought that they should fulfil the intentions of Philip in hastening the death of Don Carlos; they agreed that the physician should inform the prince of his condition, without saying anything of the king's displeasure or of the trial, and that he should prepare him to receive the exhortations which would be made for the benefit of his soul: by these means they hoped to induce him to confess and prepare himself for death, which would put an end to his misfortunes.

The Prince of Evoli held a conference with the Doctor Olivares. He spoke to him in that mysterious and important manner which persons versed in the politics of courts know so well how to employ, when it is necessary to further the views of their sovereign, or their own designs. Rui Gomez de Sylva was perfect in this art, according to the opinion of his friend Antonio Perez, the first secretary of state, who was well acquainted with all that passed. In one of his letters he says, that after the death of the Prince of Evoli, there would be no one but himself initiated in these mysteries.

Olivares perfectly understood that he was expected to execute the sentence of death pronounced by the king; and that it was to be done in such a manner, that the prince's honour should not be affected; in short, that his death was to appear natural. He therefore endeavoured to express himself, so as to inform the prince of Evoli that he comprehended him, and considered it as an order from the king.