Hyakunen Renbo

From Mousou Scans:

Eva, a long-lived witch, takes in Fernest kingdom’s fifth prince, Louis, when she is asked to heal the first prince of an illness. Although witches are traditionally despised, Louis forms a close bond with her. When Louis is called back to the palace by a strange twist of fate to take his father's place on the throne, Eva must decide whether to let him go or follow.