The Holy Roman Emperor and King of Spain are rumored to have been killed by a French plan.
One of the most powerful men of the 16th century was Charles, who ruled over a vast empire that took in much of western Europe and the Americas for more than 40 years.
The letter written in 1547 by the emperor to his ambassador in France was deciphered by a team from the research lab in eastern France.
Francis I, the Renaissance ruler who brought Leonardo da Vinci from Italy, ruled over Spain and France during a time of war and unrest.
The collection of the Stanislas library in Nancy contained a letter from Charles V to Jean de Saint- Mauris.
After much searching, Cecile Pierrot was able to find out about it in 2021.
She told reporters that it was at once mysterious andincomprehensible.
Pierrot was able to find distinct families of some 120 symbols used by Charles V.
She said that the emperor replaced vowels with marks in whole words and that it was probably inspired by Arabic.
He used symbols that didn't mean anything to confuse the adversary.
When Pierrot made out a phrase in the letter, the team was able to crack the code.
She said that there was a breakthrough that happened in one day and that they had the right hypothesis.
There was a letter from Jean de Saint- Mauris where the receiver had a form of transcription code in the margin.
It was rare for a historian to read a letter that hadn't been read for hundreds of years.
She said that it confirms the degraded state in 1547 of relations between Francis I and Charles V.
She said that relations were tense between the two.
There was a rumor of an assassination plot against Charles V that was said to have been going on in France.
She said that the monarch's fear was underscored by the plot's lack of information.
She said the researchers hope to identify other letters between the emperor and his ambassador to have a picture of Charles V's strategy in Europe.
The historian said that there will be many more discoveries in the future.
Agence France- Presse.