A SWEET NIGHT WITH HIS MAJESTY THE KING: THE NEW BRIDE WANTS TO BE DRENCHED IN HER GROOM'S LOVE

Princess of Goldwyn, Lutecia, has had feelings for Lord Valery, emperor of friendly nation, Reynald, since she was a young girl. Never having forgotten the promise his Lord Valery made to her 10 years ago, Lutecia, on her 17th birthday, devises a certain plan to put an end to her unrequired love. But...? (Source: MangaPlaza) — Description from AniList community (anilist.co).