Until now, her letters to Fersen were almost exclusively limited to matters of state. The more personal sections were carefully redacted by a mystery hand - thought to be the count himself or his descendants, in a bid to preserve her honour. All previous attempts at deciphering the censored messages, meticulously obscured by circular scribbles, proved fruitless.
However, a team at France's Research Centre for the Conservation of Collections, CRCC, has managed to extract the original handwritten text, using cutting-edge scanners.
News of the revelations follow the publication of a book by British historian Evelyn Farr, which suggests her daughter, Sophie, who died as an infant, was fathered by Fersen.
In I Love You Madly - Marie-Antoinette: The Secret Letters, she also questions the paternity of Marie-Antoinette's son Louis Charles.
The book cites the count as telling the queen: "I love you and will love you madly all my life."
"I love you madly' - you don't say that to a good friend. It implies a physical relationship. They were lovers," said Farr.