In 1217, Berengaria's brother Ferdinand III had inherited the throne of the Kingdom of Castile through abdication of their mother. In 1223, John of Brienne, aged 53, visited Santiago de Compostela, as a supposed pilgrim. He was by then twice a widower. As a consequence of his visit to Santiago de Compostela, Alfonso IX invited him to marry his daughter Sancha and, presumably, through her inherit the Leonese throne. However Berengaria of Castile, a long time divorced and an inheritor in her own right of the Castilian throne, main advisor of her son Ferdinand III, offered one of her own daughters to John instead. Aging John chose Berengaria of León, from Alfonso's second marriage. The marriage took place at Toledo in 1224.
Empress
In 1229, the throne of the Latin Empire had been inherited by Baldwin II of Constantinople, a twelve-year-old boy. The barons of the Empire decided to secure the safety of the Empire by appointing a regent-Emperor for Baldwin. They chose John who accepted the assignment as a sort of Senior Tutor. In April 1229, John was proclaimed regent at Perugia. They did not arrive at Constantinople until 1231, when John was officially crowned in his new city. Baldwin II remained the junior co-emperor and only heir to the throne. By agreement, 12-year-old Baldwin had been betrothed to around 5-years-old Marie of Brienne, the daughter of John and Berengaria, since 19 April 1229 to firmly establish the dynastic alliance of the two co-emperors and the western land for Crusades also, Spain. The marriage did not take place until 1234, when Marie was about ten years old and Baldwin about seventeen. Alberic of Trois-Fontaines records that John died on 27 March 1237, aged around 61. The "Obituaires de Sens Tome" of the Abbey of Maubuisson record that Berengaria died on 12 April 1237, aged around 33, surviving her husband by only sixteen days. She is buried in a beautiful marble coffin in the Cathedral of Santiago de Compostela, Spain, but many books and tourist leaflets mention her as if she was Queen Berenguela of Castile, her mother. Other books, however, mention this coffin as being that of another Berengaria and/or other dates, her niece, daughter of her brother King Ferdinand III of Castile, sister of King Alfonso X of Castile. But this niece, Infanta Berengaria was a nun at the Monastery of las Huelgas, Burgos, of Royal patronage, where Berengaria of León's mother, Queen Berengaria of Castile, retired as a former monarch. Further, Alfonso VIII of Castile and Eleanor of England, grandparents of Berengaria of León are buried there. Much later, Ferdinand III's and Alfonso X's bodies, also at Las Huelgas, would be moved to conquered Seville's new cathedral, where they are today.
