Over two centuries after the removal of the capital to Beijing, Nanjing was destined to become the capital of a Ming emperor one more time. After the fall of Beijing to Li Zicheng's rebel forces and then to the Manchu-led Qing dynasty in the spring of 1644, the Ming prince Zhu Yousong was enthroned in Nanjing in June 1644 as the Hongguang Emperor. His short reign was described by later historians as the first reign of the so-called Southern Ming dynasty.
Try to answer this question if possible (otherwise reply "unanswerable"): What was Zhu Yousong's title?
the Hongguang Emperor