By 1793, Queen Marie Antoinette was imprisoned in the Conciergerie. In a plan formulated by friends of the Assassin Mentor, the Comte de Mirabeau, she would pin-prick a message into a piece of paper in reply to a message hidden inside the petals of a carnation.
Marie Antoinette then paid Gilbert the vast sum of 400 louis to bring the message to her allies outside the prison. Secretly a Templar agent, Gilbert revealed the plot in order to ensure the Queen's death. He also became well aware of Mirabeau's plans to free her.
For his actions, Gilbert was to be given a recognition ceremony at the Church of the Madeleine by the National Guard. Fearful of Gilbert's knowledge of Mirabeau's involvement in the plot, the Assassin Council sent Arno Dorian to eliminate him at the ceremony. Blending with the crowd, Arno assassinated Gilbert.