Gabrielle d'Estrées, duchesse de Beaufort et Verneuil, marquise de Monceaux (Gabrielle of Estreés, Duchess of Beaufort and Vernueil, Marchioness of Monceaux) (1571–1599) was a French mistress of King Henry IV of France, born at Château de la Bourdaisière in Montlouis-sur-Loire, in the Indre-et-Loire département of France.
Born a Catholic, Gabrielle realized the best way to conclude the religious wars was for Henri himself to become a Catholic. Recognizing the wisdom in her argument, on 25 July 1593 Henri declared that "Paris is well worth a Mass" and permanently renounced Protestantism. This enabled him to be crowned King of France on February 27, 1594. As a reward, Henri arranged for her marriage to M. de Liancourt to be annulled, and gave her the titles of Marquise de Monceaux and Titular Mistress of the King of France.
News of the relationship between Henri and Gabrielle did not sit well with some members of the Parisian elite, and malicious pamphlets circulated that blamed the new duchess for many national misfortunes. One of the most vicious nicknames ascribed to Gabrielle was la duchesse d'Ordure ("the Duchess of Filth").
In the succeeding years, Gabrielle became Henri's most important diplomat, using her female friends amongst the various Catholic League families to bring about peace. In March 1596, Henri gave both Gabrielle and his saintly sister Catherine a set of gold keys which bestowed upon them seats on his council. This gift pleased Gabrielle so much that she took to wearing the little keys on a chain around her neck.
Avid horseback riders, she and Henri enjoyed hunting and riding in the countryside around Paris. For seven years, she had the role of a wife and gave the King three children he willingly acknowledged, and Henri gave her the Duchy of Beaufort in 1597.
Shortly afterward, in 1598, Henri issued the Edict of Nantes, which gave the Huguenots certain rights while deferring to Catholics. Joining forces, the Huguenot Catherine and Catholic Gabrielle went to work overriding the objections of powerful Catholics and Huguenots and forcing compliance with the edict. Henri was so impressed with her efforts that he wrote "My mistress has become an orator of unequaled brilliance, so fiercely does she argue the cause of the new Edict."
After applying to Pope Clement VIII for an annulment of his marriage and authority to remarry, in March of 1599 Henri gave his mistress his coronation ring. Gabrielle, so sure that the wedding would take place, stated, "Only God or the king's death could put an end to my good luck".
Perhaps she tempted fate too much. A few days later, in early April, she suffered an attack of eclampsia and gave birth to a stillborn son. King Henri was at the Royal Château de Fontainebleau when news arrived of her illness. The next day, April 10, 1599, while Henri was on his way to her, she died in Paris after the miscarriage.
The king was grief-stricken, especially given the widely-held rumor that Gabrielle had been poisoned. He wore black in mourning, something no previous French monarch had done before. He gave her the funeral of a Queen; her coffin was transported amidst a procession of princes, princesses, and nobles to the Saint Denis Basilica for a requiem Mass. Known in French history and song as La Belle Gabrielle, she was interred at Abbaye Notre-Dame-la-Royale de Maubuisson, Saint-Ouen-l'Aumône (Val-d'Oise, Île-de-France).
A publication after her death called the "Mémoires secrets de Gabrielle d'Estrée" (The Secret Memoirs of Gabrielle d’Estrée) is believed to have been written by one of her friends.
She is the presumed subject of the painting Gabrielle d'Estrées et une de ses soeurs by an unknown artist (c.1594). Gabrielle sits up nude in a bath, holding (assumedly) Henry's coronation ring, whilst her sister sits nude beside her and pinches her right nipple. Henry gave Gabrielle the ring as a token of his love shortly before she died.
The painting now hangs at the Louvre Museum in Paris.