Sons of the Eastern Sage

The war has already started, even if the Eastern Sage Immortal Emperor knows that there are spies, there was already no time to ferret them out.

Also, leaving aside the issues of spies, that immortal king assassin used such a top-tier assassination technique that even the Eastern Sage Immortal Emperor had no way to clearly sense him. When the assassin stepped into the void, the Eastern Sage Immortal Emperor instantly knew that that immortal king had a unique law domain. When coupled with assassination techniques, that law domain was truly extremely terrifying.