One of his sons, Peter of Courtenay, Lord of Conches, accompanied Saint Louis in the Holy Land during the Seventh Crusade; he was killed at the Battle of Mansurah (1250), along with the king's brother, Robert I, Count of Artois.

They had become minor provincial lords, since the elder branch had sold most of the family's possessions in their attempt to preserve the Latin Empire in the east.

One of the descendants of Robert de Courtenay, John III of Courtenay-Champignelles, was taken prisoner by the English at the Battle of Poitiers in 1356, and later he fought alongside Bertrand du Guesclin.

The last male of the final branch died in 1733, and the family was extinguished on June 29, 1768, with the death of his niece, Helen of Courtenay, Marquise of Bauffremont (1689–1768).

They appealed to the justice and compassion of Henry IV of France; they obtained a favorable opinion of 20 lawyers from Italy and Germany, and compared themselves to the descendants of King David, whose rights were not impaired by the lapse of ages or the trade of a carpenter.

The parliament, without denying their proofs, eluded them by arbitrarily selecting St. Louis as the progenitor of the royal line.

[nb 1] A repetition of complaints and protests was repeatedly disregarded; and the hopeless pursuit was terminated in the 18th century by the death of the last male of the family.