I read spoilers on this part and I'm not ready!



Okay but I'll give it partially cause I don't want to spoil the actual reveal.
The princess (Yulikian's cousin) finds out something unusual in the palace and tries to warn her father, the Emperor about her suspicions. He doesn't believe her and somewhat reveals this about the Princess to the wrong person.
She gets killed by this person.
However the brave Princess manages to warn Yulikian about the true villain in her final moments!
I found her end so tragic. She never hated Yulikian and always admired him as her big brother.