The Prince's Love-Child

In the beginning our heroine is Guido's mistress and he's content with it but she secretly loves him. He whisks Lucy off to see his new nephew being baptized but they end up having a huge disagreement and she flies back home. However, Guido's mistress finds out she's pregnant with her prince's baby and she tells him. Naturally he insists they get married and warns her if she refuses, he will find ways to get her to agree and she is forced to sign a pre nup relinquishing custody to the royal family if they divorce. It breaks her heart to realize she must stay married to this man to keep her child. Guido finds himself falling deeper and deeper in love with her while she tries to see what pushes his buttons. In the end they are forced to admit they are in love with each other and welcome their daughter as a possible heir to the throne, if Guido's brother doesn't have any children.