
For real!
I guess the king fell for the previous empress because of the "I'm fell for the isekai villainess protag cliché" (ofc she's no isekaid girl but, if you're familiar with those kind of story the pattern of how the noble kids fell for MC is similar). The previous empress was the daughter of a count, grew up close to the king which was possible due to her close relantionship with his other close friends(prob with their current wives too since she got their support in court that made it possible for her to be empress given her lower status), m. she was known to be ahead of her time and not the type to follow court protocol. (reason why she was disliked by the conservative nobles and clergy) Anyway she got the "not like the other noble girls" charm to her that caught the eyes of the king. Anyway she was basically opposite to the current empress, a badass woman obviously but to the eye of the king, we can assume, she came across as the typical groomed fiancé that is very court and tradition focus and rigid. I bet the king didn't find charming being married for political reason too.
The current empress is simply magnificent, how could the emperor fall for another woman ?