Amaury III had attempted to solve this problem by leaving Évreux to his eldest son Amaury IV and Montfort to his youngest son Simon III.
However, Amaury IV died three years after his father, which resulted in the reunification of the two domains.
Simon III chose to side with the English king and gave him the strongholds of Montfort, Rochefort and Epernon.
Because of this, Louis VII, King of France, "could not come and go freely from Paris to Orleans or to Etampes because the Normans had been established by King Henry in the castles of the counts of Evreux[2]".
Later, Simon III was reconciled with Louis VII, who gave him custody of the Castle of Saint-Léger-en-Yvelines.