Im not sure exactly which chapter mentions it, but they randomly retconned it so that the emperor knew all along. He suddenly says he knew from the beginning after he's shot by the arrow
Somewhere between 70th and 72th chapters, he has a discussion with Empress Dowager about Chengfeng real identity
thank you! , yeah it's Chapter 90/91 after he's wounded
In this chapters they make us think its a misunderstanding. Because the emperors mother thinks, that the secret is that liu cheng feng is a man. But the emperor thinks she means the secret of "her" being the prime minister.
will the Emperor know the truth?
I think I missed it...