Hwangtaejaui Sokkupchinguro Saranamgi

When Ella finds a sickly young boy suffering from a mysterious illness in a cave, she brings him home, only for her to discover a special healing power that helps him recover. Six years later, Carl has grown into a striking young man, but to Ella, he remains like a brother… or so she thinks. Though childhood friends, what Ella doesn’t know, is that Carl is the lost crown prince of the Easton Empire, believed to have perished in a fire… and is only biding his time to make things right again. But Carl has another secret–his feelings for Ella go far beyond family…

(Source: WEBTOONS)