Maybe its bcz of true love idk But tbh what i actually think is that he was planning to kill off his brother to get the throne and she wants to still be an empress coz uk its "the highest noble woman position in the empire" so she seduced him!(๑•ㅂ•)و✧ and since fl's not berry's bitch king real daughter they treating her like i can't wait to see when she returns to destroy berry and behead them. ヾ(❀╹◡╹)ノ~
But then again uk in some countries in their royal family like when a king or prince dies his wife has to marry another "royal" within the family if she's pregnant, i think i read it somewhere on the internet, i'm not sure if its true tho. (づ ̄ ³ ̄)づ
The only good thing abt berry's king is that he doesn't have any concubines and is just loyal to his wife. I love sing sm he's my fav i ship him and sasha!ヾ(☆▽☆) at first i hated ml and shipped fl with sing but seeing his character development and his past i can't hate him anymore he had his reasons to behave like that.