Charles was persuaded (if not ordered) to go to Russia as "Lia de Beaumont" - his own sister.  He was dispatched with expensive dresses of the latest Parisian fashion (no doubt carefully tailored to enhance his figure) and forged documents proving "her" parentage and patronage.  In early 1756 the 27 year-old Mlle Lia de Beaumont travelled to St. Petersburg to see Elizabeth as the travelling companion of a fur trader named Douglass.  Once d'Eon arrived at Elizabeth's court, he/she charmed the Empress and was granted a private interview.  During this, d'Eon discarded his female disguise and revealed himself to be the special envoy of King Louis XV, delivering to her a letter from Louis which proposed a secret agreement.

Elizabeth was so captivated by d'Eon's disguise and daring that Lia was appointed as her Reader, and was thus able to spend many hours in the company of the Empress - and perhaps became her lover.  D'Eon persuaded the Empress to write to Louis and invite a new ambassador to Moscow, and a short time later she signed a secret pact with Louis not to aid George II.  The treaty with Russia which the English ambassador had confidently expected, never happened. 

Lia took a very strong liking to this highly pampered feminine lifestyle, and the new and intriguing young French Lady-in-Waiting did not lack for male admirers within the Russian court.  However the French Foreign Ministry noted that D'Eon slept (i.e. shared a room and a bed) with a young lady who was later to become the Princess d'Askoff.  D'Eon apparently behaved as a "chaste and innocent female virgin" toward his roommate - although it's very hard to believe that he was successful in keeping his secret for six months.

By August 1756 d'Eon was back in Paris (breaking a leg during his hasty journey) to report his incredible success.  Extraordinary, only the next year he was re-dispatched to Moscow by Louis XV in his male role - fulfilling the position of Assistant to the Ambassador.  He was introduced to the Russian court as the brother (some reports say uncle) of the girl, Lia, that he had posed as the previous year!

Both Charles and his supposed sister Lia quickly became an accepted part of the English Court (perhaps even the lover of Queen Sophia-Charlotte, wife of King George III) and of the social scene around London, but of course they were never seen together!  Charles' lifestyle was sumptuous, he enjoyed fully his high position and he spent much money to create the right connections with English counts, dukes, and lords.  From vineyards in his own estate or neighbouring districts he imported and gave away as gifts Burgundian wine.  This generosity made him very popular among aristocratic wine connoisseurs but it, and the need to maintain two separate lifestyles, was costly.  Unfortunately Lia's feminine lifestyle was perhaps even more costly than Charles masculine one, and soon d'Eon was deeply in debt.  When the French Foreign Minister refused to pay the bills d'Eon began using his position to gather powerful documents on France, including some of the country's most dangerous secrets.  He accumulated these as ammunition, putting them aside in a private cache, they would also allow him the luxury of being very impudent to the new ambassador when he arrived ... .

D'Eon had not been long in his important position as Minister Plenipotentiary when he lost the favour of his sovereign, chiefly - according to his own account - through the adverse influence of Madame de Pompadour, who was jealous of him as a secret correspondent of the King.  Louis still liked to amuse himself by carrying on secret schemes of fantastic diplomacy through subordinate agents, behind the backs and without the knowledge of his responsible ministers.  The Duc de Choiseul, Minister of Foreign Affairs, and the Marshal de Belle-Isle, Minister of War, were both kept in the dark, as was perhaps more importantly Madame de Pompadour.

D'Eon was thus soon superseded by the Comte de Guerchy and was informed that he would have to give up the title of Plenipotentiary Minister.  D’Eon showed his irritation by denying the genuineness of the Comte's letter of appointment and complaining of his treatment to a number of influential friends.  But nobody helped him.  In October 1763 he refused to follow orders to leave England.  Apparently d'Eon was afraid that he would be kidnapped and taken to France and in a letter to Louis XV he claimed that the Comte de Guerchy had tried to have him poisoned: "Subsequently I have discovered that M. de Guerchy caused opium, if nothing worse, to be put in my wine, calculating that after dinner I should fall into a heavy sleep, that they would put me, still asleep, onto a couch and, instead of my being carried home, I should be carried down to the Thames where probably there was a boat waiting ready to abduct me."   Indeed d'Eon raised an action against Guerchy for the alleged attempt to poison him.  Guerchy, on the other hand, had previously commenced an action against d’Eon for libel, founded on the publication by the latter of certain state documents of which he had possession in his official capacity.  Both parties succeeded in so far as a true bill was found against Guerchy for the attempt to murder, though by pleading his privilege as Ambassador he escaped a trial, and d’Eon was found guilty of the libel.  Failing to come up for judgment before the court in France when called upon, he was outlawed. 

In 1766 a forgiving Louis XV granted d'Eon an annual pension of 12,000 livres for the services that he had rendered to the King in Russia in the army and other commissions.  D'Eon continued to work as a spy, but he also had another hobby - books.  During his London residency he spent much of his time and money on his library, which eventually contained some 6,000 books and 500 rare manuscripts. 

Also in 1766, in another small twist of his complicated and secretive life, d'Eon became a Freemason in the Lodge of Immortality, No. 376, which met at the Crown and Anchor Tavern in the Strand, London, England.  He served as a Junior Warden in 1769 and 1770.

After Louis XV's death in 1774 the new King, Louis XVI, called d'Eon back to France for the purpose of acquiring d'Eon's stolen document collection and permanently removing the embarrassing Chevalier from the scene.  The deeply in debt d'Eon reacted by sending messages from his secret London hideaway to Paris trying to blackmail the new King by threatening to disclose his spying activities.  He demanded that Louis XVI bestow a considerable amount of money on him, as well as provide his written guarantee that he would be protected from his enemies in France before he gave up his office.  Unless his terms were met, d'Eon threatened that he would reveal to the English all his secret correspondence with Louis XV, and the clandestine French plans to invade England.  This set a royal dilemma as the new King had been making secret overtures to be on friendlier terms again with the English, as the cost of various wars was crippling the French (and other) economies. 

An improbable view of the negotiations between Beaumarchais and d'Eon is depicted in the French movie Beaumarchais, l'insolent.  Actress Claire Nebout plays a tall, beautiful and slim d'Eon with whom Beaumarchais flirts, in reality the rather short d'Eon was by then middle-aged (47), plain in appearance, and distinctly stout!

In April 1775 Louis XVI sent his top agent, Pierre Augustin Caron de Beaumarchais, to England to negotiate the release of the sensitive documents.  For the attempted blackmail the Chevalier should have gone to prison, and Charles could not allow his advisors to see there was no punishment - so a unique solution was found which conformed to d'Eon's own demand that the government publicly recognise him as a woman.  The Chevalier would be paid for spying services rendered, a sum of money more than adequate to cover all his debts, and he would be allowed to return to France and live there freely - providing he did so ONLY as a woman!  His prison sentence was only suspended in case he tried to revert to being Charles, and with this threat hanging over him, he would cause the King no further trouble.  This solution provided a further safeguard because even when 'she' was back in France, Charles could not readily dare risk the discovery by the English of 'his' duality and 'her' high level spying.

D'Eon accepted the king's royal guarantee of safety and an amount of money that would be used to pay the spy's creditors, also his old pension of 12,000 livres was restored (with interest for missed payments) and to paid quarterly.  He then turned over the secret documents and in 1777, age 49, returned to France to live out his life in France as a woman in accordance with the secret edict that Louis had decreed: "Charles Genevieve Louise Augusta Timothee d'Eon de Beaumont is hereby commanded to lay aside the uniform of a dragoon, which he had been in the habit of affecting, and resume the garments of her sex; and is forbidden to appear in any part of our kingdom in any other garments than those suitable to a female".  By the end of 1777 d'Eon was legally a woman in both and England and France - no longer a Chevalièr but a Chevalière!

The low cut dresses of eighteenth century court fashion were apparently not a problem for Lia as her good bust was often commented upon at the time.  Confusingly, other pictures show her as a relatively flat chest'ed woman. so padding and artistic license seems possible.

D'Eon was granted funds for the expensive wardrobe required by a lady of fashion, and Marie-Antoinette sent Mademoiselle D'Eon some corsetieres, courtiers and maids to wait on her. The French Queen further insisted that D'Eon be the centre of interest wherever s/he went, to be presented at court, and be invited to the drawing rooms of the foremost hostesses of Paris and Versailles.   In pictures of the period he is often depicted in relatively comfortable clothes, skirts, and low heels instead of high heels of women.  On his left breast d'Eon always carried the Cross of Saint-Louis.

As "Lia's" years went by and the need for secrecy passed, the conditions became increasingly onerous to the Chevalier, and time and again this swash buckling hero appeared at the palace of Versailles in breeches, only to be whisked off by the palace guards and re-dressed in ladies' clothes - often tied in such a way that Lia found them almost impossible to get off again without the aid of servants.

In 1785 d'Eon was again found in violation of his agreement after he was seen riding across the grounds of his estate in his old dragoons uniform.  He was ordered to never again move about unless he was dressed as female. 

The same year, four years before the French Revolution, d'Eon was given permission to visit London in order to put his affairs there in order, and for the purpose of bringing back his library and other property.  Hinted in this was the possibility of other undisclosed documents, potentially embarrassing to France.  So France effectively sent d'Eon on his/her way, along with a gift of 6000 livres.  Setting up house again in London, d'Eon would spend the rest of his life of his life in England.  England was for him "a country more free than Holland and well worthy of being visited by a man of thought and lover of liberty...".  D'Eon chose to arrive as "Lia" - a surprising decision given that his rebellion against wearing female clothes had caused him so many problems in France.  Indeed "Charles" was never to re-appear, d'Eon living the last twenty years of his life entirely as a woman, ironically d'Eon had finally made a gender choice in favour of the fair sex just when the march of time was making him unable to pass as a woman.  When Horace Walpole met d'Eon in 1786 he found him loud, noisy, and vulgar - "her hands and arms seem not to have participated of the change of sexes, but are fitter to carry a chair than a fan."  And James Boswell wrote that "she appeared to me a man in woman's clothes."

D'Eon helped supported himself by opening up a successful fencing school.  But he cut an odd figure while teaching young Englishmen the art of swordplay - he was at all times dressed as a woman.  In 1787, d'Eon sought extra income by challenging to a duel a champion swordsman also from France and living in London at the time.  The match took place at Carlton House in London on the 9th April before an audience of the Prince of Wales and many members of the fashionable sporting world.  Though nearly sixty and now rather corpulent, d'Eon triumphed over a competitor twenty years his junior while wearing three tiers of skirts and a lady's lace cap.

After this victory D'Eon gathered a small supporting company of fencers and began to tour the provinces giving displays of skill in packed public halls. 

In 1789, with the outbreak of the French Revolution, d'Eon's pension ceased and despite selling his huge library to cover part of his debts he spent seven months in debtors prison. 

In 1792, perhaps in desperation, he strangely sent a letter to the National Assembly in France and volunteered "to fight and die for the nation, the Law, and the King", and to lead a division of women soldiers against Austria.

In 1795 D'Eon made the acquaintance of a Mrs Mary Cole, whose husband had been an admiral, and they were to live together for the next fifteen years.

In August 1796 D'Eon's small company was performing in Southampton, where an opponent's broken foil pierced his side.  Badly wounded, he was bedridden for two years and was never to recover his strength.  Sadly d'Eon's final years were spent in poverty and misery.  In 1805 he signed a contract for his autobiography, entitled La Pucelle de Tonnerre, but this was never published. Perhaps to protect the reputation of Mary and other lady friends who trusted him going back to his days as a spy, he did not complete this and reveal his true sex.

D'Eon passed away peacefully in his bed on May 21, 1810, after having spent about 49 years living mostly as a man, and then another 33 years living as a woman.  Upon his death, a number of English gentlemen insisted that the 81-year-old body of d'Eon be examined to settle long-standing wagers as to whether or not he was a woman.  Most lost the bet.  The coroner who examined the corpse reported that the clever French spy was not a hermaphrodite or a woman but was a man.  However he also reported:

"The body presented unusual roundness in the formation of the limbs, the appearance of a beard was very slight, the throat was no means masculine; shoulders square and good; breasts remarkably full; arms, hands, fingers, those of a stout female; hips very small and legs and feet corresponding to the arms".

It was only now that d’Eon’s friend, Mrs Cole, discovered (an unlikely and belated revelation) that her housemate of so many years was in fact a man.  

D'Eon was buried in the St. Pancras Old Church cemetery in England, where his/her tombstone is still present today.

The mainstream view of most of d'Eon's biographers is that he was physcially male but a tranvestite, perhaps even transgender.  However, a contrary view advocated by a few historians is that d'Eon was born female but was brought up male by his family due to their desperate need for a male heir to the estate. This would explain his/her consistent ability to pass physically as a woman - even when sharing a bedroom as a young 'lady', and in old age as an invalid.  The coroner's report is arguably not decisive evidence, but it does explicitly state that d'Eon was male - to resolve the bets?  Only an exhumation of d'Eon's skeleton for DNA testing (if suitable material remains) is likely to resolve his/her sex definitively. 

Biographies:

• La Vie Militaire, politique, et privée de Mademoiselle d'Eon by La Fortelle (1779);

• The True Story of the Chevalier d'Eon by E.A. Vizetelly (1895); D'Eon de Beaumont: His Life and Times by Octave Homberg (1911);

• La vie étrange de la chevalière d'Eon by Armand Charmain (1929);

• The Chevalier d'Eon 1728-1810 by Marjorie Coryn (1932); L'Estrange Destinée du chevalier d'Eon 1728-1810 by Pierre Pinsseau (1945); D'Eon: chevalier et chevalière by André Frank (1953);

• Royal Spy: The Strange Case of the Chevalier d'Eon by Edna Nixon (1965);

• The Enigma of the Age: The Strange Story of the Chevalier d'Eon by Cynthia Cox (1966);

• Le Chevalier d'Eon et son problème psychosexuel by M. Cadéac (1966);

• Monsieur d'Eon Is a Woman by Gary Kates (1995); Monsieur d'Eon by Mark Brownell (2001);

• The Maiden of Tonnerre: The Vicissitudes of the Chevalier and the Chevaliere D'Eon (2001)

• Normal Woman, by Philippa Gregory (2023)

For further information: - The Beaumont Society - Chevalier d’Eon (1728-1810)

Other primary documentary sources:

• Essai historique sur les differentes situations de la France par rapport aux finances sous le regne de Louis XIV et la regence du duc d'Orléans, 1753

• Mémoires pour servir à l'histoire générale des finances, 1758 (2 vols.)

• Note remise à son excellence Claude-Louis-François-Regnier, comte de Guerchy..., 1763

• Lettres, mémoires, et négociations particuliéres, 1764

• Nouvelles lettres du chevalier d'Eon, 1764

• Dernière lettre du chevalier d'Eon de Beaumont à M. le comte de Guerchy, en date du 5 août 1767, 1767

• Les Loisirs du chevalier d'Eon de Beaumont..., 1774 (13 vols.)

• Pièces rélatives aux démélés entre Mademoiselle d'Eon de Beaumont... et le Sieur Caron, dit de Beaumarchais, 1778

• Très-humble réponse à... Beaumarchais, 1778

• Réponse de Mademoiselle d'Eon à Monsieur de Beaumarchais, 1778

• Epître aux Anglais dans leurs tristes circontances présentes, 1788