Celine: As a real princess, although you have no control over your marriage, you have to strive for your own happiness.
Karl: Although she is an unknown aristocrat disguised as a man (at least at first), she has more power than a man to get close to Celine.
The encounter in the library allowed Celine to meet the person she loved, and she loved her without looking back.
Angels under the sun, "boys" behind roses, that's what they are.