What Does The Da Vinci Code Say About The Last Supper?

The Da Vinci Code, a mystery novel, refers to Da Vinci's paintings The Last Supper and the Mona Lisa.  Dan Brown's character Robert Langdon says that The Last Supper is unusual because the character seated to the left of Jesus is female.  

Brown thinks this character is Mary Magdalene, because Jesus knew Mary Magdelene personally in the Gospels.

Other art historians say that the character is actually the disciple John.  Christians say, if that person is Mary Magdelene, then the disciple John, whom Jesus was close to, is completely missing from the painting.

The character is definitely feminine in his/her appearance.  He/She has somewhat long hair, blondish hair, a white, small face, delicate facial features, and maybe the hint of female breasts.

However, it is important to know that the Priory of Sion, which Brown says Da Vinci was a member of, was "discovered" by three French academics in the 20th century, and 2 of them have said that they invented it themselves.

He says that the person to the right of christ is a woman, mary Magdalene, when in fact they were all supposed to be men