Pietro de Medici was a Florentine nobleman and the cousin of Queen Catherine de Medici and Francesca de Medici. In 1557, Pietro and Francesca came to their cousin's aid by convincing the Pope not to allow for King Henry II of France to legitimize his eldest son Sebastian de Poitiers, but Henry responded by seeking his imprisoned wife's execution upon his return. Pietro and Francesca later left a poisonous seed with their cousin to provide her with a clean death if she did not wish to be beheaded, and they told her that she had disgraced the House of Medici.