  Émilie le Tonnelier de Breteuil, marquise Du Châtelet-Lomont—or simply Émilie Du  Châtelet—was born in Paris on 17 December 1706 to baron Louis Nicholas le Tonnelier de Breteuil and Gabrielle Anne de Froullay, Baronne de Breteuil. She married Marquis Florent-Claude de Châtelet-Lomont in 1725. Together they had three children, a daughter and two sons (the second died the year after his birth). In 1733, she met Voltaire who became her lover and life-long intellectual companion. They retired to Du Châtelet's husband's estate—Cirey—which was remodeled to include a laboratory with several instruments for their on-going scientific experiments. In 1748, she became pregnant at the age of 42 with the child of her then lover, Jean-François de Saint-Lambert. She bore her fourth child, a daughter, on 4 September 1749 and died on 10 September 1749.