Agnes was Princess of Navarre and a close relative of both the English and Frankish royalty.
She was second cousin to the Black Prince and great granddaughter of Henry III.
In her early life she had a love affair with Guillaume de Machaut and is said to have inspired and been the subject of his poem le Voir Dit. Marchaut was a priest who was also famous as a composer of both martial and religious music. he would have come in contact with Agnes when he was offered the patronage of Agnes’ brother Charles II of Navarre.
Agnes hereself wrote poetry, probably under the influence of Guillaume.
Agnes’ marriage to Gaston de Foix was an arranged marriage which was beset with difficulty.
The marriage was typical of Gaston’s political aptitude and ruthlessness.
Agnes was the grandaughter of King Louis X of France(subject to the doubts about her mothers legitimacy). her brother Charles married Jeanne the daughter of KingJean II of France This contact could have been used by Gaston if the negotiations with the English had failed; which indeed they did.
Agnes is the initial catalyst for Ximene seeking assistance from Blanche d’Evreux.