While he may have seen himself primarily as a French prince, particularly early on, the focus of the Navarrese foreign policy during Charles III's reign gradually shifted towards Navarre's neighbours in the Iberian Peninsula.

Charles skillfully secured a balanced web of alliances through the marriages of his sisters and daughters to French lords and Iberian princes, ensuring a long-lasting peace in Navarre.

[1] His parents were there on one of their long stays, managing the County of Évreux and other fiefs during the first phase (1337–1360) of France's Hundred Years' War against England.

When in January 1363 it was her turn to move to Navarre, Queen Joan left Charles in the custody of his aunt Blanche, sister of his father and widow of his maternal great-grandfather King Philip VI of France.

[2] On 27 May 1375, in the Castilian town of Soria, Charles married Eleanor, daughter of King Henry II of Castile, sealing the peace between their fathers.

[8] Eleanor played a key role in securing Charles's release in 1381 by having her brother King John I of Castile exert diplomatic pressure on France.

She and their daughters joined him in Navarre upon his accession, but the new queen soon fell gravely ill. She returned to Castile as soon as her health began to improve and took the princesses with her.

Eleanor did not find this sufficient, but the death of her brother John and the accession of her nephew King Henry III of Castile, who was less sympathetic to her cause, forced her to compromise.

[15] In 1393, Charles procured a link to the Aragonese royal house by arranging for his sister Marie to marry Duke Alfonso II of Gandia.

The same year, he secured the return of Cherbourg from the English and started negotiations with the French court about the settlement of his claims on land in France, which resulted in the exchange of the counties inherited by his father for various rents and the Duchy of Nemours.

Charles III took an active part in European affairs as a prince of the blood of the royal house of France until 1406, after which he reoriented himself towards the Iberian Peninsula.

[10] Charles excelled in diplomacy: much of the peace and prosperity Navarre enjoyed during his reign can be attributed to the matrimonial alliances he forged with his nobles and rulers in Iberia and southern France through his numerous female relatives.

The selection of the third daughter, Blanche, ahead of her older sisters suggests that either Martin or Charles, or both, were not keen on creating a personal union between their kingdoms.

Charles concurrently negotiated the marriage of Joan, his eldest daughter, with John, heir apparent to the County of Foix; the king may have preferred that Navarre be the primary partner in any potential union.

[17] These two marriages, as well as that of Beatrice, the fourth daughter, to Count James II of La Marche in 1406, put a strain on Charles's coffers, and his struggle to pay their dowries led to disputes with their respective in-laws, particularly the king of Aragon.

[18] Charles entrusted the kingdom to Eleanor and their daughter Joan from 1408 to 1411, when he was seeking compensation from the French royal court for lost territories.

[20] The death of his childless eldest daughter, Joan, in July 1413[17] prompted Charles to seek a closer match for Blanche, who became the new heir presumptive.

Charles refused Joan's widower's proposal to marry Blanche and instead in mid-1414 offered her in marriage to Alfonso, the eldest son of the new king of Aragon.

[22] The change may have been prompted by Burgundy's alliance with England, where Charles's sister Joan was imprisoned on a charge of witchcraft after the death of her second husband, King Henry IV.

[23] In 1416, following the examples of the kings of France, Castile, Aragon, and Portugal in dealing with the Western Schism, Charles III stopped recognizing the Avignon-based Benedict XIII as the true pope and switched his allegiance to Gregory XII, who ruled in Rome.