The Supreme Elder of the Sun and Moon Divine Sect was originally Louu Jiangyou, but after Louu Jiangyou caused trouble and was killed, the Supreme Second Elder Nian Sijing took his place.
Ye Zhen knew about Nian Sijing's arrival at Red Fire Martial City. Originally, according to Ye Zhen's request, there was no need for a King of the Establishment Realm to get involved in such trouble only to end up dying.
However, Sect Leader Jian Qianxiong said in a talisman communication that he had other plans, instructing Nian Sijing to arrive first and help Ye Zhen hold Red Fire Martial City. As long as they held out for a few more days and his injuries recovered somewhat, he could send more people over.
Jian Qianxiong indeed had great foresight. Nian Sijing's early arrival spared Ye Zhen a lot of trouble. Without him overseeing the situation, Ye Zhen would not have been able to cultivate peacefully for three days.