Impostor
Agis Stirlander still couldn't believe that the Third Prince he had been interacting with and divulging information was someone else all along, an impostor.
But all the facts pointed towards the Third Prince he had been interacting with is obviously fake.
In the world of cultivation, subordinates wouldn't usually suspect their masters as it was the other way around. They usually followed orders and tried to be loyal unless they had rebellious intentions in their mind.
Agis Stirlander is a loyal subordinate, hence, from the start, he didn't have much doubt since he hadn't detected much difference as the impostor behaved nearly to how the Third Prince would behave.
Hence, this also made him think that the impostor should be someone closer to the Third Prince but the thing is... The Third Prince didn't put on airs like a grand person but instead interacted with others as if they were his peers.