In 1227 the Livonian Brothers of the Sword conquered all Danish territories in Northern Estonia. After the Battle of Saule the surviving members of the Brothers of the Sword merged into the Teutonic Order of Prussia in 1237 and became known as Livonian Order. On 7 June 1238, by the Treaty of Stensby, the Teutonic knights returned the Duchy of Estonia to Valdemar II, until in 1346, after St. George's Night Uprising, the lands were sold back to the order and became part of the Ordenstaat. After the conquest, all of the remaining local population were ostensibly Christianized. In 1535, the first extant native language book was printed, a Lutheran catechism. The conquerors upheld military control through their network of castles throughout Estonia and Latvia. The land was divided into six feudal principalities by Papal Legate William of Modena: Archbishopric of Riga, Bishopric of Courland, Bishopric of Dorpat, Bishopric of Ösel-Wiek, the lands ruled by the Livonian Brothers of the Sword and Dominum directum of King of Denmark, the Duchy of Estonia.
Question: How many years after the Livonian Brothers of the Sword conquered all Danish territories in Northern Estonia did the Teutonic knights returned the Duchy of Estonia to Valdemar II,?
Answer: 11