The allegations, published by the Times of London, are from historian Philippe Collas, whose great grandfather was the magistrate who sent her to the firing squad.
The Dutch-born woman, whose real name was Margareth Gertrude Zelle, arrived penniless in Paris in 1904 and took up exotic dancing, quickly rising to star status.
With the advent of the war, the dancer was offered money by a German officer to sleep with French soldiers to elicit information -- an offer she reportedly accepted.
But then in 1917, Collas says she switched sides, sleeping with German officers to supply the French with information.
The book claims the French secret services needed to pull off a high-profile coup to distract attention from their bungling in the first three years of the first world war. So Zelle was arrested, charged with treason and shot after a trial behind closed doors.
Matas says his great-grandfather, who had recently discovered his wife was unfaithful, ordered Zelle put to death.
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