@A_12 It’s because
Spoiler!
princess Scandia (ML) is Ibex's son who is Empress Tigria's lover before she was forced to marry the trash Emperor. So in order to not get her kid get killed by Emperor she dresses up her son as a girl. And her second son is the only legitimate heir to throne whom she gave birth as a duty being an Empress but she loves both her sons equally.
I like to post spoilers for the stories I find interesting because I don't have much time to read novel due to busy schedule you will find me in most romantic historical manhwa comment sections