
Rashta had a very depressing past, but instead of making good use of her experiences, she let her greed guide her. She wasn't very intelligent, but she's cunning when she wants something. I almost cried for her children. Her first born was so beautiful, and the Emperor truly did love her second child. But then I guess, it's better to have the story go the way it is now, at least, the Empress got what she truly deserve.

SPOILERS ALERT!
The chapters I read was not translated well so I can't assure that my answer is 100 percent accurate.
A faternity test was held for the princess (the child Rashta is carrying now in the webtoon) and the Emperor. The results showed that the princess was not the Emperor's daughter and instead was Rashta's past lover( the one who abandoned Rashta). Also, It seems like Rashta asked Duke Elgy( or something, he's the duke and seems to be Heinley's close friend, and also the man who lent Rashta money) to kidnap or hide her first born (Anh) or have someone kidnap(?) him, any way that can get Anh far from the Emperor. But then Duke Elgy came up on the scene, carrying Anh. Everyone has there attention on the Princess and the fact that Rashta deceived the Emperor so I couldn't
really say anything about their reaction when Anh showed up, and with the Emperor too, but I'm sure that he was really upset, like really really upset.
That is the only scene I've read where Anh was shown to the public, but I think there was a scene where the real father bought Anh to Rashta, but I'm not too sure, but eother the father or the grandfather gifted Rashta with his son's hair, and the Emperor saw the hair inside the envelope and knew that it's not Rashta's hair, unlike to what she said that she cut her hair out of boredom.
Another is, Koshar (Empress' brother), delivered an information to the Emperor that Rashta had a child. Koshar knew this after beating up the grandfather of Anh and forcing him to tell him Rashta's weakness. This lead to the Emperor ordering for Koshar's banishment because the emperor is trash and stoopid. He wants to cover up for Rashta.
About the Emperor's reaction, he had information about Rashta's past, but the translation was hard to read so.... I guess he was wary and his suspicions on Rashta grew. And when Duke Elgy showed up with Anh during the Faternity test, there was no significant reaction from the Emperor, or maybe it's just the translation.
Sorry if it's too long, I tried to give anything that I remember that is connected to the first born.
AND FEEL FREE TO CORRECT ME PLSSS
I binged read the whole series, and I'm forgetting a lot of parts.
The novel is actually a good read. I've finished reading the available chapters and dang, it was satisfying fo see how things go. The emperor was such a pitiful lad, really. Pitiful, but I'd say he deserves it. I don't really know if the Rashta did something that made the Emperor like her so much, but what he did to the Empress was idiotic.