The bone, a piece of cloth and a cat femur were said to have been recovered after the 19-year-old was burned in 1431 in the town of Rouen. In 1909 - the year Joan of Arc was beatified - scientists declared it "highly probable" that the relics were hers.
But starting last year, 20 researchers from France, Switzerland and Benin took another look. Even they were surprised to find the rib bone came from an Egyptian mummy. Their best guess is that the fake was cooked up in the 19th century, perhaps to boost the process of Joan of Arc's beatification. She was canonized as a saint in 1920 by the Roman Catholic Church.
In medieval times and later, powdered mummy remains were used as medicine "to treat stomach ailments, long or painful periods, all blood problems," Philippe Charlier, who headed the research team, told The Associated Press.
The team's assumption is that a 19th-century apothecary transformed "these remains of an Egyptian mummy into a fake relic, or fake historic remains, of Joan of Arc," he said.
Tests dated the rib bone to between the 7th and 3rd centuries B.C., he said. The cat bone dated from the same period and also was mummified. The researchers also found pine pollen, probably from resin used in Egyptian embalming, he said.