The evil Isabelle, the Marquise of Chaussin
Isabelle, the Marquise de Chaussin was the hidden main villainess from "The Jewel in the Crown," the penultimate episode of Bones' eleventh and penultimate season (airdate July 14, 2016). She was the wife of Henri, the Marquis de Chaussin, as well as the episode's murder victim.
During the Jeffersonian's investigation, French Inspector Rousseau appeared and identified the victim as Isabelle, the Marquise de Chaussin, while voicing his belief that she was murdered by her husband. In addition, Isabelle's murder was believed to be committed to a pair of jewelry store robberies; one in France, the other in the US, and Henri was suspected of robbery as well. The revelation of a woman being one of the robbers led to Blake Masters, a young woman who accompanied Henri, being suspected; however, the group inspected the surveillance video of the robbery, and while Dr. Temperance Brennan concurred that one of the robbers was female, it was not Blake, with further inspection of the body revealing that the female robber was none other than Isabelle.
Henri revealed in the episode's climax that, with Blake's help, he had sold their jewelry collection to keep up the prestige that went with the title; however, Isabelle turned heel by resorting to robbery to regain their jewels. The villainess committed the robberies with her illicit lover, Chadwick Grey, who killed his scout during the robbery in France. After arriving in America, the evil Isabelle approached jewelry store saleswoman Eve Mayweather and stated that she had known about her daughter's condition and need to pay for her medical bills, leading to Eve becoming a conspirator in the villainous couple's robbery of her store.
In spite of her role as a villainous robber, Isabelle had promised Eve that no one would be hurt, and she lashed out at Chadwick for killing his scout and planned to turn him in for the murder. In response, an angry Chadwick strangled Isabelle to death.