King Zhaoxiang of Qin
Because King Zhaoxiang had not yet legally come of age (traditionally at the age of 20), his mother, who was now known as Queen Dowager Xuan, became the regent. She was supported by her brothers, Wei Ran and Mi Rong (羋戎), as well as two other sons, Prince Yi (公子悝) and Prince Fu (公子巿), the four of them collectively known as the "Four Nobles" (四貴).
King Zhaoxiang of Qin
In 307 BC, Ying Ji's older half-brother, King Wu, unexpectedly died after breaking his shin bones while trying to show off his physical prowess by lifting a heavy bronze cauldron in the Zhou palace at Wangcheng. King Wu died young and childless, hence placing the state of Qin into a succession crisis, with a number of princes now eligible to claim the throne. At the time, Prince Ji was still a hostage in the state of Yan, and was generally considered unlikely to be a candidate. However, King Wuling of Zhao decided to take advantage of the situation and intervene in the domestic politics of his western neighbour. King Wuling ordered his chancellor of the Dai Commandery, Zhao Gu (趙固), to smuggle Prince Ji out of Yan into Zhao territory, before endorsing him to return to Qin and contest for the throne. Furthermore, Prince Ji's maternal uncle, Wei Ran (魏冉), was a general in command of a significant Qin military forces, and helped suppressing most of his nephew's political opponents. This enabled Prince Ji to successfully claim the throne as the King Zhaoxiang of Qin at the age of 18.