Antoine III de Croÿ, Prince de Porcien (1540-1567) was a French noble and Protestant rebel. Porcien, who held the rank of prince through his sovereign possessions, was a member of the Croÿ family. In 1558 his mother converted to Protestantism, and he followed her in 1560. His house, de Croÿ had been close with the Guise who used them as part of their broader rivalry with the House of Montmorency, supporting their claims that hurt their rival. Porcien broke with the Guise after his conversion. With the advent of Francis II's reign he joined Navarre in opposition to their house. The following year a strategic marriage was arranged for him with Catherine de Clèves which would bring him the County of Eu in 1564.
Porcien's castle Montcornet, raised to a principality in 1561
Catherine of Cleves, Countess of Eu was the wife of Henry I, Duke of Guise and the matriarch of the powerful and influential House of Guise. By marriage, she was Duchess of Guise from 1570 to 1588, and Dowager Duchess of Guise thereafter. She was also Countess of Eu in her own right from 1564.
Catherine of Cleves