The Italian Woman by Jean Plaidy
"The second book in the classic Catherine de’ Medici trilogy from Jean Plaidy, the grande dame of historical fiction When Catherine de’ Medici was forced to marry Henry, Duke of Orleans, her heart was not the only one that was broken. Jeanne of Navarre once dreamed of marrying this same prince, but, like Catherine, she must comply with France’s political needs. And so both Catherine’s and Jeanne’s lives are set on unwanted paths, destined to cross in affairs of state, love, and faith, driving them to become deadly political rivals.
Years later Jeanne is happily married to the dashing but politically inept Antoine de Bourbon. But the widowed Catherine is now the ambitious mother of princes, and she will do anything to see her beloved second son, Henry, rule France. As civil war ravages the country and Jeanne fights for the Huguenot cause, Catherine advances along her unholy road, making enemies at every turn".