Jacques of Savoy, duke of Nemours was - in my opinion, anyway - a player. At one point he had several high-born women bickering over him - a contemporary source writes "like washerwomen" (considered one of the lowest classes of people) - and not just any women either: the parties involved were Françoise de Rohan (cousin of the Queen of Navarre, Jeanne III, and member of the Huguenot branch of the Rohan family), Anna d'Este, duchesse de Guise and Lucrezia d'Este, later duchess of Urbino.
It all came down to the principle of honor vs word. Jacques had married Françoise in secret, and they'd lived as husband and wife. But he had been sent to Italy and while there, he'd reportedly made promises of marriage to Lucrezia d'Este. When he returned to France, he married (bigamously to some minds) the now-widowed duchesse de Guise.
When Françoise protested against this marriage, it turned into a very seamy lawsuit, penetrating to such high strata of society as Catherine de Medici (accosting Françoise for her "loose living"). Finally, it was decided that Jacques had "only" been engaged to Françoise (who had believed it to be a genuine marriage, and the son she had by Jacques, Henri, bore the surname "de Savoie" until his death), and that the marriage to Anna was good and valid.
However, this matter had some serious implications for the legal system in France, leading to the discredit of the value of honor, and the insistence on a priest from the parish of both parties being present at the wedding vows to avoid such situations as secret marriages (another one was the heir of the duc de Montmorency who married Diane de France, bastard daughter of Henri II, but had previously contracted a secret marriage). But at the heart of the matter also lay the feud between the Catholics (d'Este, Nemours, Guise, Valois) and the Huguenots (Rohan, Navarre).
But what if the court which divorced Jacques and Françoise (Rome acknowledged the marriage as invalid, but it took a bit longer and a bit more meddling from the king in France to dissolve it) had been acknowledged as valid? What might the implications, legal, religious and political, be for France's future?