In 1583, feeling deceived by the Court and King of France Henry III, he seizes the city by surprise. In response, pretexting a request from Henry of Navarre to secure commercial communications between Bordeaux and Toulouse on the Garonne against acts of piracy, a royal garrison is established in Bazas.
Fearing for his authority and government in Guyenne, Henry of Navarre protests to Henry III, who wishes to establish garrisons in Condom, Agen, and Casteljaloux. According to Henry of Navarre, this is an attempt to confine him in Nérac, where nothing will be free, not even his person. Especially Casteljaloux, the former city of the Lords of Albret, was strategic as it allowed to resist the enterprises of the Catholic forces in the north of the duchy of Albret.
Henry therefore alerted the city at the end of 1583: "having heard that those of Bazas are planning to carry out a certain enterprise. We cannot think that it is not on our city of Casteljaloux, of which we wanted to warn you, so that you take even better care and prevent their plan.
" Methodical and wise man of war, Henry of Navarre anticipated and also ordered his soldiers to defend his city, the former city of the Lords of Albret, against the Catholic Royal forces. His authority, government, and security were at stake.
"Captain Portal, I send you the advice I received about a plan by those from Bazas against the town of Casteljaloux, which makes me ask you to act quickly against them, taking on your way the men of piety of Captain Pichart to whom I write by this carrier so that he assists you with all his. I have no doubt that you will thwart this plan with your usual courage and I hope for a new proof of your devotion to the good of my service. Your most affectionate master and friend.
François de Pichard, lord of the Nasse, captain of Gironde and Castelmoron, served Henry of Navarre for a long time in the company of the gendarmes of Henry who, to reward him for his good services, gave him the hereditary captaincies or governments of Gironde and Castelmoron. In 1575, he was sent as a negotiator for a truce between the kings of France and Navarre.