A U.S. historian specializing in the Italian Renaissance claims to have cracked the mystery of Mona Lisa's famous smile.

The secret, according to William Varvel, is that the woman in Leonardo da Vinci's iconic painting was a feminist.

The Mona Lisa, or La Gioconda in Italian, was a feminist who lived during the 1500's. Varvel claims the woman was a supporter of gender equality in the Catholic Church.

"La Gioconda was trying to get people to see that the New Jerusalem would be here as soon as you recognize women's theological rights," Varvel told AFP, according to The Local.  "La Gioconda may be a grand statement for women's rights."

Varvel, 53, presents his theory in his new book, "The Lady Speaks: Uncovering the Secrets of the Mona Lisa." It took Varvel, who is from Texas, nearly 12 years to complete his theory behind La Gioconda.

Varvel argues that da Vinci intentionally painted the last chapter of the book of Zechariah from the Old Testament in several of his works, the Mona Lisa included.

"Leonardo constructed and placed a total of 40 separate symbols taken from chapter 14 into the background, middle ground and foreground of the composition of the Mona Lisa," Varvel said according to The Local.

For example, folds on the sleeves of Mona Lisa's arms indicate a yoke, a device used for domesticated animals like oxen. This suggests women's oppression, The Local reported.

Zechariah's  book announced the coming of a New Jerusalem, which da Vinci believed was "based upon a universal recognition of both men and women of the laity to have recognized rights of the priesthood of Jesus Christ," Varvel said, The Local reported.

"The perception of the New Jerusalem is the secret that her smile reflects."

La Gioconda is from the name of Lisa del Giocondo, the woman in da Vinci's painting that was completed in 1515. Del Giocondo came from an aristocratic family in Florence. Her husband, a merchant of cloth and silk, ordered the painting, according to The Local.