A BL fiction about how a boy entered the imperial harem to replace his sister and end up having the Emperor fall for him

Please read book 1 to not spoil the ending. Please it driving me nuts when you don't add both to your reading lists! The second book to "The Male Concubine" During his days as the Crowned prince, Hong Er after a battle that he lost, he was then taken as hostage but managed to escape since was deeply wounded in the mountains he was saved by a beautiful hermit who took care of him and he fell in love the his caretaker. Once he ascended the throne his first action was to search for him. After years of searching he finally found him but how can he persuade a man that gave up all his worldly desires? And can that man adjust to the inner palace?