From His mistress to his wife

The queen has a sister no one knows about. She's sick and dying, the only choice she has is to train her sister to be her and take over.

They started out as orphans but a duke comes and takes one, leaving the other. Annetta must take care of her sister in secret once she is taken.

The king needs a lady to pleasure his son, and the duke volunteers Annetta. Soon the prince falls in love with her, taking her to be his wife.

No one must know Annetta is now dying so her and the king get her twin sister to take her place. But just like before, the now king, has fallen in love with his mistress.

What happens when the queen finds a witch to cure her but the king doesn't want her anymore?