The Evil Prince and his Precious Wife

It's hard to understand why she didn't have another child. She's not barren, so shouldn't she be able to give birth to another child that is MJ's child? Well, she's happy in the end even though her new hubby is unable to perform his sexual duty. 

She melted in the pool of her own poison. It was in a mountain retreat, forgot why they went there (due to summer heat, i think?), but the emperor was there along with YYC, the fiancee(forgot name), YYC's mother, and some of their friends. But that is where, the fiancee really knew that YYC doesn't love her anymore and is driving her out in favor of MX. So she became crazy and decided to retaliate. First using vampire-esque mosquito that MX discovered is weak to fire. Then zombies, then i think is then she revealed that she, Qin Yuyuan(?), did in fact knows martial arts and she transformed nto sone kind of monster. Her true target is MX, but of course both OS and YYC joined to protect her and kill the QYY. Somehow a barrie was erected to limit the fight between the 4 of them, so the friends cannot help. The battlefield is within the area of the pond(?), that has really corrosive water, so MX decided to bring out the tiger(?)-wood machine that she previously snatched from a country they visited before. With that they managed to defeat the princess causing her to fall into the water, thus melting off her everything.

Actually, in that instance, you can sort-of have premonition about the emperor's having further interest to MX.

Hope that helps.  

Is she really that stupid? 

Thanks @ChuChi, I was worried but now, it's relieving to know that the crown prince is not as stupid as to fall for her words so easily. 

HuThanks,and his wife cheated on him with a eunuch 

Yes, that was before he became a eunuch. They were actually supposed to be married but before that happened, his family got punished and he became a eunuch. It was only after that they discover the pregnancy but still the aunt still married Murong Jian(?). I don't know what she did to trick him in their wedding night but she passed her pregnancy as a premature baby of MJ. 

He was at first really confused, afterall he was injured and still in recovery, but after the emperor's judgement, he was still calling MJ "father" until MJ told him that he is not his son. Then he was devastated when he realized the situation, especially when he thought about before he was so high in society as a Murong son but now a lowest peasant. After that they were just hiding in a small dilapitated courtyard. 

I'm curious about that as well