These years saw an evolution in the participation of Empress Dowager Cixi (Wade–Giles: Tz'u-Hsi) in state affairs. She entered the imperial palace in the 1850s as a concubine to the Xianfeng Emperor (r. 1850–1861) and came to power in 1861 after her five-year-old son, the Tongzhi Emperor ascended the throne. She, the Empress Dowager Ci'an (who had been Xianfeng's empress), and Prince Gong (a son of the Daoguang Emperor), staged a coup that ousted several regents for the boy emperor. Between 1861 and 1873, she and Ci'an served as regents, choosing the reign title "Tongzhi" (ruling together). Following the emperor's death in 1875, Cixi's nephew, the Guangxu Emperor, took the throne, in violation of the dynastic custom that the new emperor be of the next generation, and another regency began. In the spring of 1881, Ci'an suddenly died, aged only forty-three, leaving Cixi as sole regent. 

What was the name of Xianfeng's concubine?