Teresa of Leon is sometimes referred to as Teresa of Portugal
Teresa of Portugal (1181 – June 18, 1250), also known as Tarasia of Portugal, was the oldest daughter of Sancho I of Portugal and wife of Alfonso IX of Castile.
Teresa was the mother to three of Alfonso's children, but when her marriage to Alfonso was declared invalid because of a discovered familial link which proved them to be cousins, she returned to her familial home of Lorv„o , Portugal. There, she founded a benedictine monastary. Soon after, she converted the monastary into a large Cistercian convent, replete with over 300 nuns.
In 1230, Alfonso died after having several children with a second wife, Berenguela of Castile. This second marriage was also annulled because Berenguela was Alfonso's second cousin. With two invalid spouses, there was dispute among the children as to who would inherit the throne. Teresa stepped in and allowed Ferdinand III of Castile, Berenguela's first son, to take the throne of Leon.
After the succession battle, Teresa returned to Lorvao and finally took her convent vows after years of living as a nun. She died in the convent on June 18, 1250 of natural causes.
In 1705, Teresa was canonized by Pope Clement XI, along with her sister, Sanchia of Portugal .
Teresa's Catholic feast day is June 17th.