Doesn't look like the former king was a great parent anyways. Didn't even care enough to educate his inheriting son about the nature of the relationship with her. Seems like all he was told was that they had a powerful vampire vassal that could be used in case of emergencies.
It HAS been 15 generations since she "assisted" King Harvard I in founding the kingdom. That's 400 or 500 years at about 30 years per generation. Much has been forgotten, it would seem. And you know what they say about people who forget history...