The disintegration of the Pagan Empire was now complete. But the Mongols refused to fill in the power vacuum they had created. They would send no more expeditions to restore order. The emperor apparently had no interest in committing troops that would be required to pacify the fragmented country. Indeed, his real aim all along may have been "to keep the entire region of Southeast Asia broken and fragmented." It would be another two years until one of Narathihapate's sons, Kyawswa, emerged as king of Pagan in May 1289. But the new "king" controlled just a small area around the capital, and had no real army. The real power in central Burma now rested with the three commander brothers. The uneasy arrangement would persist until 1297. The Mongols continued to occupy northern Burma to Tagaung as the province of Zhengmian  but ended the fictional central Burma province of Mianzhong on 18 August 1290. Meanwhile, the power struggle in central Burma continued with the three brothers blatantly consolidating support. To check their rising power, Kyawswa submitted to the Mongols in January 1297, and was recognized by the Yuan emperor Temür Khan as King of Pagan on 20 March 1297. The emperor also gave Chinese titles to the brothers as subordinates of Kyawswa. The brothers resented the new arrangement as it directly reduced their power. On 17 December 1297, the three brothers overthrew Kyawswa, and founded the Myinsaing Kingdom. The dethronement forced the Mongol government to intervene again, leading to the second Mongol invasion of Burma . The invasion failed. Two years later, on 4 April 1303, the Mongols abolished the province of Zhengmian , evacuated Tagaung, and returned to Yunnan.
Question: When did Zhengmian become King of Pagan?
Answer: Kyawswa submitted to the Mongols in January 1297, and was recognized by the Yuan emperor Temür Khan as King of Pagan on 20 March 1297