CNN  — 

Redacted lines from letters between Marie-Antoinette and her alleged lover have been revealed for the first time, using advanced scientific techniques.

The letters, exchanged by the doomed French queen and Count Axel von Fersen of Sweden during the French Revolution, were analyzed by a team of scientists from the Centre de Recherche sur la Conservation (CRC) in France, who published their findings in the journal Science Advances on Friday.

The Bruker M6 Jetstream XRF scanner during the analysis of the letter of September 26, 1791 written by Queen Marie-Antoinette to von Fersen

“Whether state secrets, escape plans, or evidence of a royal love affair, this presumably sensitive content has been puzzling historians for almost 150 years,” reads the study, which also details how von Fersen helped organize a failed attempt to smuggle the royal family out of France.

Some of the letters between the pair, sent from June 1791 to August 1792, are held in the French national archives.

Certain words in the letters had been written over with random letters designed to obscure them.

The team analyzed sections of 15 different letters, and found consistent differences in the copper-to-iron and zinc-to-iron ratios of inks in eight of them.

The scientists used x-ray fluorescence spectroscopy, which is used to determine the elemental composition of materials, and data processing techniques to reveal the hidden words, such as “beloved,” “tender friend,” “adore,” and “madly.”

The scanner during the analysis of a letter written on October 25, 1791 by von Fersen to Marie-Antoinette

Analysis showed that some of the letters thought to have been written by Marie-Antoinette were in fact copies of originals sent by von Fersen. This was common practice at the time, when “copies of important letters could be made for political or administrative reasons,” according to the study.

In addition, all of von Fersen’s letters had similar ratios of ink elements, which matched with some of the ink used to redact words.

This points to the possibility that von Fersen was responsible for censoring the letters between himself and the wife of King Louis XVI, “suggesting that they were important to him either for sentimental or political reasons,” CRC said in a press release.

The researchers hope their techniques can be used to unveil more redacted historical content.

Marie-Antoinette is famed as the last queen of France before the revolution.

In March 1791, her jewelry was wrapped and placed in a wooden chest and smuggled out of France to Vienna by a loyal retainer for safekeeping.

Both Marie-Antoinette, an Austrian archduchess by birth, and her husband, Louis XVI, were executed by guillotine in October 1793. Their son died in captivity shortly afterward at the age of 10.

In November 2018, a pearl and diamond pendant from the queen’s private collection fetched more than $36 million at auction, smashing pre-sale estimates that had valued it between $1 million and $2 million.