He had been appointed admiral, and subsequently marshal; and had even been entrusted with the command of the King's armies at the siege of Amiens, where he bore the title of marshal-general, although several Princes of the Blood and the Connetable himself were present.

He was decorated with all the Royal Orders; was a duke and peer of the realm, and Governor of Bordeaux; and, in fine, every attainable dignity had been lavished upon him; while he yielded precedence only to royalty, and to the Duc de Montmorency, to whose office it was vain to aspire during his lifetime.[177] Such was the Marechal de Biron, when, in the vainglorious hope of one day becoming the sovereign of certain of the French provinces, he voluntarily trampled under foot every obligation of loyalty and gratitude, and leagued himself with the enemies of his royal master, to wrest from him the sceptre which he so firmly wielded.

The first intelligence of the Duke's defection which reached the monarch--to whom, however, his conduct had long appeared problematical--was obtained through the treachery of the Marechal's most trusted agent; a man whom Biron had constantly employed in all his intrigues, and from whom he had no secrets.

This individual, who from certain circumstances saw reason to believe that the plans of the Duke must ultimately fail from their very immensity, and who feared for his own safety in the event of his patron's disgrace, resolved to save himself by communicating the whole conspiracy to the King; for which purpose he solicited an audience, declaring that he had important matters to reveal, which involved not only the throne of the sovereign, but even his life; and he so confidently insisted upon this fact, that an interview was at length accorded to him at Fontainebleau; where, in the presence of Henry and the Duc de Sully, he confessed that conceiving himself to have been ill-used by the Court, he had from mortified vanity adopted the interests of M.de Biron, and even participated in the conspiracy of which he was now anxious to anticipate the effects, and from which he had instantly retired when he discovered that it involved the lives of his Majesty and the Dauphin.
He then solemnly asserted that when the Marechal de Biron proceeded to Flanders to receive the oath of peace from the Archduke Albert, the Spaniards, who at once detected the extent of his vanity and ambition, had flattered his weakness and encouraged his hopes; and that they had ultimately despatched to him an individual named Picote, who for some crime had been exiled from Orleans, and who was authorized to give him the assurance that it only depended upon the Duke himself to secure a brilliant position through their agency, should he see fit to become their ally.

The Marechal, his associate went on to say, listened eagerly to the proposition, and expressed his willingness to treat with Spain whenever it might be deemed expedient to confide to him the real meaning of the message; a reply which satisfied the Spaniards that with proper caution they should find it no difficult undertaking to attach him entirely to their interests, or, failing in this attempt, to rid themselves of a dangerous adversary by rendering him the victim of his own treason.
Elated by the brilliant prospect which thus opened upon him, Biron gradually became less energetic in the service of his legitimate master; and after the peace of Vervins, finding his influence necessarily diminished, he began to murmur, affecting to believe that the services which he had rendered to the sovereign had not been duly recognized; and it was at this period, according to his betrayer, that their acquaintance had commenced, an acquaintance which so rapidly ripened into friendship that ere long he became the depository of his patron's most cherished secrets.
After many and anxious consultations, principally caused by the uncertainty of the Duke as to the nature of the honours which were to be conferred upon him, it had been at length resolved between the two conspirators that they should despatch a priest to the Duke of Savoy, a monk of Citeaux to Milan, and Picote himself to Spain, to treat with the several Princes in the name of the Marechal; and what was even more essential to the monarch to ascertain, was the fact that a short time subsequently, and before he visited Paris, the Duke of Savoy had entered into a secret negotiation with Biron, and even led him to believe that he would bestow upon him the hand of one of his daughters, by which marriage the Marechal would have become the cousin of the Emperor of Germany, and the nephew of the King of Spain, an alliance which, to so ambitious a spirit, opened up an opportunity of self-aggrandizement never to be realized in his own country and under his own sovereign.
In return for this concession, Biron had pledged himself to his wily ally that he would provide so much occupation for Henry in the interior of his kingdom, that he should have no leisure to attempt the invasion of the marquisate of Saluzzo, a pledge which more than any other gratified M.de Savoie, who lived in constant dread of being driven from his territories.