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A new book suggests that Marie Antoinette had two illegitimate children with a Swedish diplomat.

Historian Evelyn Farr has spent the last 20 years writing about the love affair between the young French queen and the SwedeAxel von Fersen. Her latest book, I Love You Madly, revolves around a new trove of letters, which Antoinette wrote to her lover during the 20 years they carried on their affair. According to Farr, the couple used an elaborate system of invisible ink and secret codes to disguise their messages. 

Farr told People on Thursday that she now has convincing proof that Fersen also fathered two of Antoinette’s children: Louis Charles, who would have succeeded Louis XVI as king of France, and Princess Sophie. Both children died before reaching adulthood. 

In the years leading up to the French Revolution, the press wrote that Antoinette, who had left her native Austria at 14 to marry the French dauphin, had had affairs with several aristocrats, including the Marquis de Lafayette and the English Baroness Lady Sophie Farrell. Historians have largely found the allegations exaggerated, and the allegations about her affair with von Fersen difficult to confirm. These new letters may provide evidence to the contrary. 

In one from early 1792, Antoinette wrote: “I am going to close, but not without telling you, my dear and very tender friend, that I love you madly and never, ever could I exist a moment without adoring you.”