The extra one was Prince Yiyang, Liu Chang.
Prince Yiyang Liu Chang was also Liu Ziyue's uncle. When Chu Yu first saw this name, she thought his name was Liu Yongri, but she later realized that "Yongri" was supposed to be read together, not as "Yongri" but as "Chang".
Liu Chang, who held military power, was a regional commander. Even before Liu Ziyue succeeded to the throne, Liu Chang was quite disliked by his own elder brother, the Emperor, and was constantly suspected of planning rebellion. He lived in trepidation until Liu Jun died and Liu Ziyue ascended the throne, whereupon he remained the number one suspect of intending to rebel.
Emperors are innately very suspicious creatures, not to mention that this suspicion is somewhat hereditary.
