It might not have been cheating. It wasn't unusual for real world kings in the past to have multiple wives and concubines. All a bit messed up but royalty in general does a lot of weird stuff with the excuse it is traditional.Okay that queen may be a bitch but the king is worse for cheating on the queen then deciding to put his daughter as his successor who seems to have no education to run the country.
It was most likely cheating if the guy didnt bring the daughter close to the family but instead sent her to commoner family. If it was traditional then at least the king could protect said daughter and raise her under said rules.It might not have been cheating. It wasn't unusual for real world kings in the past to have multiple wives and concubines. All a bit messed up but royalty in general does a lot of weird stuff with the excuse it is traditional.