Hartwell House, owned by the same Lee family as that from which Robert E. Lee was a descendant, was indeed hired by the Bourbons, who essentially trashed the place. It is now a hotel.
Louis Stanislas, the portly Comte de Provence, reigned as King Louis XVIII of France after the Restoration until his death in 1824 (with a minor hiatus for the brief return of Napoléon from Elba). Provence’s comment about the “ninety-eight percent,” while sounding startlingly modern, was actually a point often made at the time. He was succeeded by his brother, the Comte d’Artois, who reigned as King Charles X. Charles’s ultraroyalist, pro-Jesuit policies—encouraged by Marie-Thérèse—helped spark the Revolution of 1830.
Marie-Thérèse died childless in 1851 and is buried at the Franciscan convent of Castagnavizza in what is now Slovenia. She reigned as Queen of France for twenty minutes in 1830.
The small French chapel near Portman Square was real but is no longer in existence. Originally dedicated to Notre Dame de l’Annonciation, it was later renamed in honor of St. Louis. At one time, there were some thirty bishops and eight thousand French priests living in exile in London.
The outstanding authority on homosexuality in Georgian England is Rictor Norton. He has most generously published his material online, at http://rictornorton.co.uk. His articles on the molly underground in London are fascinating and provided the background for my portrayal of Serena Fox.
There actually is a legend about a Dark Countess who was reputed to be the true Marie-Thérèse. Known in German as the Dunkelgrafen and in French as the Comte et Comtesse des Ténèbres, the “Dark Counts” were a wealthy, reclusive couple who took refuge in Thuringia. The man called himself “Count Vavel de Versay,” but the woman’s identity was kept a secret. When the “Countess” died in 1837, she was buried with unseemly haste. The doctor who attended her death reported that she appeared to be about sixty years of age, which would have put her birth around that of Marie-Thérèse.
The count was eventually shown to be Leonardus Cornelis van der Valck, a Dutch diplomat at one time attached to the embassy in Paris. But speculation about the identity of his companion persists. Rumors linking the Dark Countess to Marie-Thérèse began as far back as the Princess’s 1799 marriage to the Duke of Angoulême. The mysterious pair are enduringly popular in Germany; there is even a Madame Royale Historical Society dedicated to them, complete with lecture symposiums.
A word about titles of nobility: While it might seem strange to American ears, the wife of a duke’s younger son would indeed be known by “Lady His-First-Name,” or Lady Peter. Likewise, although logically one would expect Hero to be called “Hero St. Cyr,” in conversation she would actually be known by her own first name combined with her husband’s title, “Hero Devlin.” Consider, for instance, the famous “Sally Jersey,” who was the wife of George Villiers, the Fifth Earl of Jersey.