Newly decoded letters penned by Marie-Antoinette suggest France's last queen had a torrid affair with a Swedish count and two of the children she had with Louis XVI were illegitimate.

Two centuries after she was guillotined during the revolution, researchers have unlocked the secrets of blacked-out secret passages from her letters to Axel de Fersen, a friend of the royal family. The first of 13 extracts reads: "I will end [this letter] but not without telling you, my dear and gentle friend, that I love you madly and that there is never a moment in which I do not adore you."

Dated January 4, 1792, it was penned in black ink six months after the count unsuccessfully tried to spirit the captive royals out of Paris. A year later, Louis XVI was executed.

Historians have long debated the nature of the relationship between Marie-Antoinette and Fersen - romantic, sexual or merely platonic.

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The question was a crucial at the time as revolutionaries depicted the queen as a frivolous thief and a traitor to husband and country while royalists insisted she was loyal.

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.