https://www.britannica.com/event/Battle-of-the-Thirty
According to the visitors' guide to the Chateau de Josselin "As evening fell that day, the victor, Captain de Beaumanoir, returned the prisoners to Josselin and had them executed."
https://en.wikipedia.org/wiki/Combat_of_the_Thirty#Battle
https://www.britannica.com/event/Battle-of-the-Thirty