The Princess Of Cortova by Diane Stanley:
Molly, Alaric and Tobias return to share a final adventure that will intrigue, sadden and ultimately satisfy admirers of their earlier escapades (The Cup and the Crown, 2012, etc.).
Having gained his throne (though it’s still a bit precarious) and possession of a magical loving cup, Alaric has decided to strengthen his position by courting his brother’s widow to create an alliance between the countries of Westria and Cortova. He’s unhappy, to say the least, when he discovers that his uncle (and rival for the crown) seeks to marry his son to the princess. The return of this former adversary as well as the introduction of two clever and unpredictable characters whose intentions and alliances are unclear keeps the suspense high despite the length of the text and the fact that much of the action is relatively subdued.