Do you still think that's MM in the "Last Supper?" Bruce Boucher of the Art Institute of Chicago three years ago dealt with the question:
. . . it also leaves readers wondering: how much does this murder mystery have to do with the real Leonardo? The short answer is not much, and the author's grasp of the historical Leonardo is shaky. One small but telling point comes in Mr. Brown's references to Leonardo as "Da Vinci," as if that were the painter's last name, yet it is no surname but simply a reference to the fact that he was the illegitimate son of Ser Piero of Vinci, in the Florentine territory. Like other great artists, with or without last names, Leonardo is invariably referred to by his given name and not by da Vinci.
The nomenclature suggests a lack of familiarity with the copious bibliography on the painter, as do Mr. Brown's references to Leonardo's "enormous output" of Christian art and "hundreds of lucrative Vatican commissions." Leonardo was, in fact, notorious for his meager production and spent little time in Rome. Neither, for that matter, is it accurate to call Leonardo a "flamboyant homosexual": despite a charge of sodomy against him as a young man, the evidence of his sexual orientation remains inconclusive and fragmentary. Thanks to "A Penitent Blogger"