iunior Duke of Slavonia (1220–26) The senior king ceded the lands between the Adriatic Sea and the Dráva River—Croatia, Dalmatia and Slavonia—to Béla in 1220. A letter of 1222 of Pope Honorius III reveals that "some wicked men" had forced Andrew II to share his realms with his heir. Béla initially styled himself as "King Andrew's son and King" in his charters; from 1222 he used the title "by the Grace of God, King, son of the King of Hungary, and Duke of all Slavonia". Béla separated from his wife in the first half of 1222 upon his father's demand. However, Pope Honorius refused to declare the marriage illegal. Béla accepted the Pope's decision and took refuge in Austria from his father's anger. He returned, together with his wife, only after the prelates had in the first half of 1223 persuaded his father to forgive him. Having returned to his Duchy of Slavonia, Béla launched a campaign against Domald of Sidraga, a rebellious Dalmatian nobleman, and captured Domald's fortress at Klis. Domald's domains were confiscated and distributed among his rivals, the Šubići, who had supported Béla during the siege. Duke of Transylvania (1226–35) King Andrew transferred Béla from Slavonia to Transylvania in 1226. In Slavonia, he was succeeded by his brother, Coloman. As Duke of Transylvania, Béla adopted an expansionist policy aimed at the territories over the Carpathian Mountains. He supported the Dominicans' proselytizing activities among the Cumans, who dominated these lands. In 1227 he crossed the mountains and met Boricius, a Cuman chieftain, who had decided to convert to Christianity. At their meeting, Boricius and his subjects were baptized and acknowledged Béla's suzerainty. Within a year, the Roman Catholic Diocese of Cumania was established in their lands. Béla had long opposed his father's "useless and superfluous perpetual grants", because the distribution of royal estates destroyed the traditional basis of royal authority. He started reclaiming King Andrew's land grants throughout the country in 1228. The Pope supported Béla's efforts, but the King often hindered the execution of his son's orders. Béla also confiscated the estates of two noblemen, brothers Simon and Michael Kacsics, who had plotted against his mother. Béla's youngest brother, Andrew, Prince of Halych, was expelled from his principality in the spring of 1229. Béla decided to help him to regain his throne, proudly boasting that the town of Halych "would not remain on the face of the