1799 Sep. 14 Quintero, Father Isidro New Orleans, (Louisiana) Alexos Sasie [Alexandre Louis Le Sassier, baptised March 3, 1753], native of New Orleans appeared and swore that he knew the child, Luisa, as the illegitimate daughter of Luis Decluet [born Louis Jean Laurent Broyner de Clouet on February 6, 1766] and Clara [Lopez] de la Pena [born April 1, 1778], daughter of [Jose] Lopez de la Pena [Captain of infantry, native of Pontevedra, Galicia, Spain] and Luisa Mandevill known as Brunet, [Louise de Marigny Mandeville aka Brunet]daughter of Mr. Mandevill, an officer in the service of France and Maria Juana a mestiza, daughter of a white man and an Indian without any mixture of colored or mulatto blood. Sasie is 53 and signs as Alexo Lesassier. A.D.S. (Spanish)
The key phrase is "Mr. Mandevill, an officer in the service of France." By my estimates, Mandeville would have to have been born before 1744. Antoine Pierre Philippe de Marigny de Mandeville was born July 17, 1721 at Fort Louis de la Mobile in current Mobile, Alabama, and died November 6, 1779 in New Orleans. He is buried in the St. Louis Cathedral. He married Francoise Jacqueline Louise de Lisle Dupart on January 8, 1748 in New Orleans.
Since Antoine's eldest son, Pierre Enguerrand Philippe de Marigny de Mandeville, was born June 15, 1751, my estimate of a birth for Mr. Mandeville prior to 1744 rules his eldest son out. Antoine's two other brothers died as small children, and so the only son of Francois Philippe de Marigny de Mandeville [1682-1728], Antoine's father, was apparently the only Mandeville in Louisiana at that time.