Ernestine de Lambriquet born as Marie-Philippine Lambriquet (31 July 1778- 31 December 1813), was the adoptive daughter of Louis XVI of France and queen Marie Antoinette.
She was the daughter of Philippine Lambriquet, a married chamber maid at the royal palace of Versailles. She was regarded to have a physical resemblance to the King and to his daughter Marie Thérèse of France, and there has been speculations that she was the illegitimate daughter of Louis XVI of France. She was chosen by the queen to be the playmate of princess Marie Thérèse and always in the latter's company. Upon the death of her mother, she was formally adopted by the royal couple 9 November 1788, and awarded a pension of 12.000 livres by the king. She slept in the same room as Marie Thérèse, was educated with her and treated as a royal child by the royal governesses.
During the French revolution, she accompanied the royal family from Versailles to the Tuileries in Paris. During the Flight to Varennes, she was sent to her father in the country, but was returned after the royal family was brought back to Paris. Upon the 10 August (French Revolution), Marie Antoinette ordered the royal sub-governess Renée Suzanne de Soucy to bring her to safety, and during the reign of Robespierre, she was taken care of by the family of de Soucy's father, the Mackau family.
Ernestine Lambriquet, under the name of Marie Philippine Lambriquet, married a widower called Jean-Charles-Germain Prempain, a proprietor in Paris on 7 December 1810. She died on the 30 December 1813, in Saint Denis Arrondissement, Paris, aged 35. The death certificate records her parents as Jacques Lambriquet and Marie Philippine Noirot. There were no children.
Lambriquet was not the only adoptive child of the royal couple, who adopted three children except her: "Armand" (Francois-Michel Gagné), an orphan adopted in 1776; Jean Amilcar, a Senegalese, in 1787; and Zoe, the motherless daughter of a servant, adopted in 1790.
The Switch Theory
A theory persists that Marie-Thérèse of France, daughter of Louis XVI and Marie Antoinette, escaped from imprisonment in the Temple during the French Revolution, and swapped identities with her adoptive sister, Ernestine Lambriquet.
Theories as to why and how Marie Thérèse escaped the Temple abound. She is thought to have been exchanged for prisoners, been raped and got pregnant, or through trauma and wanting to disappear.
According to the theory, she became the 'Dark Countess', who resided at Hildburghausen in Thuringia, Germany. The Dark countess, called Sophia Botta by the Count she was living with, only went out in public with a veil over her face or in a carriage. She died at Hildburghausen on 28 November 1837, and was buried quickly without public fuss. Her companion, Leonardus Cornelius Van Der Valck (called the Dark Count) lived there until his death on 8 April 1845.