Catherine de' Medici
Reign of Henry III

Two years later, Catherine faced a new crisis with the death of Charles IX at the age of twenty-three. His dying words were "oh, my mother..." The day before he died, he named Catherine regent, since his brother and heir, Henry the Duke of Anjou, was in the Polish–Lithuanian Commonwealth, where he had been elected king the year before. However, three months after his coronation at Wawel Cathedral, Henry abandoned that throne and returned to France in order to become King of France. Catherine wrote to Henry of Charles IX's death: "I am grief-stricken to have witnessed such a scene and the love which he showed me at the end... My only consolation is to see you here soon, as your kingdom requires, and in good health, for if I were to lose you, I would have myself buried alive with you."

Henry was Catherine's favourite son. Unlike his brothers, he came to the throne as a grown man. He was also healthier, though he suffered from weak lungs and constant fatigue. His interest in the tasks of government, however, proved fitful. He depended on Catherine and her team of secretaries until the last few weeks of her life. He often hid from state affairs, immersing himself in acts of piety, such as pilgrimages and flagellation.

Henry married Louise de Lorraine-Vaudémont in February 1575, two days after his coronation. His choice thwarted Catherine's plans for a political marriage to a foreign princess. Rumours of Henry's inability to produce children were by that time in wide circulation. The papal nuncio Salviati observed, "it is only with difficulty that we can imagine there will be offspring... physicians and those who know him well say that he has an extremely weak constitution and will not live long." As time passed and the likelihood of children from the marriage receded, Catherine's youngest son, Francis, Duke of Alençon, known as "Monsieur", played upon his role as heir to the throne, repeatedly exploiting the anarchy of the civil wars, which were by now as much about noble power struggles as religion. Catherine did all in her power to bring Francis back into the fold. On one occasion, in March 1578, she lectured him for six hours about his dangerously subversive behaviour.

In 1576, in a move that endangered Henry's throne, Francis allied with the Protestant princes against the crown. On 6 May 1576, Catherine gave in to almost all Huguenot demands in the Edict of Beaulieu. The treaty became known as the Peace of Monsieur because it was thought that Francis had forced it on the crown. Francis died of consumption in June 1584, after a disastrous intervention in the Low Countries during which his army had been massacred. Catherine wrote, the next day: "I am so wretched to live long enough to see so many people die before me, although I realize that God's will must be obeyed, that He owns everything, and that He lends us only for as long as He likes the children whom He gives us." The death of her youngest son was a calamity for Catherine's dynastic dreams. Under Salic law, by which only males could ascend the throne, the Huguenot Henry of Navarre now became heir presumptive to the French crown.

Catherine had at least taken the precaution of marrying Margaret, her youngest daughter, to Navarre. Margaret, however, became almost as much of a thorn in Catherine's side as Francis, and in 1582, she returned to the French court without her husband. Catherine was heard yelling at her for taking lovers. Catherine sent Pomponne de Bellièvre to Navarre to arrange Margaret's return. In 1585, Margaret fled Navarre again. She retreated to her property at Agen and begged her mother for money. Catherine sent her only enough "to put food on her table". Moving on to the fortress of Carlat, Margaret took a lover called d'Aubiac. Catherine asked Henry to act before Margaret brought shame on them again. In October 1586, therefore, he had Margaret locked up in the Château d'Usson. D'Aubiac was executed, though not, despite Catherine's wish, in front of Margaret. Catherine cut Margaret out of her will and never saw her again.

Catherine was unable to control Henry in the way she had Francis and Charles. Her role in his government became that of chief executive and roving diplomat. She travelled widely across the kingdom, enforcing his authority and trying to head off war. In 1578, she took on the task of pacifying the south. At the age of fifty-nine, she embarked on an eighteen-month journey around the south of France to meet Huguenot leaders face to face. Her efforts won Catherine new respect from the French people. On her return to Paris in 1579, she was greeted outside the city by the Parlement and crowds. The Venetian ambassador, Gerolamo Lipomanno, wrote: "She is an indefatigable princess, born to tame and govern a people as unruly as the French: they now recognize her merits, her concern for unity and are sorry not to have appreciated her sooner." She was under no illusions, however. On 25 November 1579, she wrote to the king, "You are on the eve of a general revolt. Anyone who tells you differently is a liar."
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