French princess and saint. Name variations: Isabel; Saint Isabelle; Blessed Isabelle. Born in March in 1225; died in 1270; daughter of Blanche of Castile (1188–1252) and Louis VIII, king of France (r. 1223–1226); sister of Saint Louis IX (1214–1270), king of France (r. 1226–1270).
Daughter of Blanche of Castile and King Louis VIII of France, Saint Isabelle was born in 1225, the youngest sister of Saint Louis IX. From an early age, Isabelle studied natural history, medicine, logic, Eastern languages, and Latin, along with the scriptures. She was known for her piety. Her brother Louis often delighted in disclosing that Isabelle was once so deep in prayer that she hardly knew her bed was being made up with her in it.
At age ten, the young princess was betrothed to the son of the count of Angoulême. Not long after, while the French court was at Saint-Germain, Isabelle grew dangerously ill, "as a result of mortifications." A holy person, brought to her bedside, prophesied that she would recover and give her life to God. Her brother Louis broke off the betrothal with 10,000 silver francs.
Then Frederick II, Holy Roman emperor, proposed that she marry his son Conrad (IV), heir to his empire. When Pope Innocent IV championed the request, Isabelle told the pope that she would rather be last in the ranks of the Lord's virgins than first in the world as empress.
In 1258, she founded the abbey of Longchamp, opposite Mount Valerian, on the right bank of the Seine. The convent, comprised of 60 nuns, mostly from the court circle, followed the rule of St. Clare of Assisi . Though Pope Urban IV moderated the rule as much as possible, Isabelle was too ill to follow the routine. Instead, she lived within the convent walls for the last ten years of her life without taking her vows, repairing clothes for the poor. She died, age 46, lying on a bed of straw. Her feast day is February 22.