Koigokoro ni Kurushimu Ouhi wa, Ikoku no Kusushi Outaishi ni Kyuuai Sareru

Luzeria, the daughter of a duke, fell in love with King Edward, married him, and became queen. However, this was a sham marriage, as the king summoned his childhood friend, the daughter of a baron, Airi, to his castle and became infatuated with her. Tired of her love for the king, Luzeria took a "love-erasing medicine" given to her by Akil, a well-known foreign pharmacist, and divorced the king. After her divorce and Luzeria returned to the dukedom, Akil began visiting her for some reason... As they got to know each other, Akil revealed that he was actually the crown prince of a great country, traveling in search of something, and that the thing he was looking for was Luzeria, and he suddenly proposed to her...!

(Source: Gaugau, translated)