One, she is the Succubus Queen.
Two, I suspect she is his mother?
Or, she is felling guilty because she will be making love to the son of her best friend and the father is the king of monsters. That means, she has not only betrayed her best friend, but may have been disloyal to her monster king! Either way, she was suppose to teach him his powers and how to defend himself, become the king of monsters, and take over the Human Queendom and restore monsters to their former glory and place in this domain!
You should be able to find out if you reach the end of the story. Maybe someone else could confim this for you.
Me, I am aiming to play though this for the second time. I last played this in version 2 or 3. We are now in version 5.3. I came back to see the changes and continue the stories of my favorite misfits and monsters!
May he (my William De Bruce) go and restore the monsters! No comprimising and having a happy ever after ending where humans keep monsters down! It is time for revolution!
Viva La Monster! Viva La Revloutiona!