Despite these increasingly sour relations, Longueville was with Guise in his departure from court that October, leaving the regency government under Catherine de Medici perilously thin in terms of support.

In 1572 he was ordered in his capacity as governor of Picardy to prevent Protestants from crossing the border to militarily assist their co-religionists in the Spanish Netherlands.

His efforts in this regard were undermined by Charles IX who covertly supported an expedition, hoping to weaken Spanish power.

[2][3] His mother was openly Protestant, and she instilled her faith in her son, who privately converted, corresponding in secret with Jean Calvin.

[8] For the wedding, Longueville ordered a suit of clothes in black velvet banded with gold embroidery sewn with pearls from a Parisian embroiderer, Guillaume Corbeau.

[3] The crown did not rush to assist with his ransom, his proximity to the Guise at a time they were in disfavour making the king ill-inclined to support him.

[12] Conscious of the religious and financial crisis facing the kingdom the Guise administration, responsible for the young François II, decided to call an Assembly of Notables.

Longueville was among the catalogue of grand nobles present, the only absentees being the renegade Bourbon princes Condé and Navarre who were conscious they would be arrested for their suspected involvement in the Conspiracy of Amboise if they showed.

[14] Longueville was among those who departed court with the end of the Guise government, as the young François II died and was succeeded by his brother Charles IX of France and a formal regency under his mother Catherine de Medici.

Despite Protestantism still being illegal in France, the seigneur de Longjumeau hosted regular services for many of the nobles of Paris in his residence.

Angry Catholic militants, frustrated at the crown allowing this to continue with their full knowledge in Paris, attacked the residence; many of the Protestant nobles caught inside during the service armed themselves in defence.

[18] The presence of Longueville in this grand exit from court indicate that religious differences with the crown were not the sole reason for disillusion with the regency government.

Montmorency joined the exodus from court, leaving a rump administration under Catherine, Navarre and a handful of Protestant councillors.

[20] As a provision of the Peace of Longjumeau the crown agreed to pay off the reiters that the Protestant rebels had hired for the campaign.

French Protestants, sympathetic for their compatriots abroad, began crossing the border in Picardie under arms to militarily support them.

The Spanish protested vehemently to the crown about this provocation, and Charles instructed Longueville to prohibit crossings of the frontier.

The king's opposition to border crossings was however circumspect and he covertly agreed to an unofficial expedition under the sieur de Genlis, however this was met with disaster and crushed by the duke of Alva.

Frustrated, the crown entrusted Longueville to reach out to La Noue, one of the leading Protestant nobles in rebellion, to convince him that a settlement was in their best interest.