The part that says "FACT".
Right after his opening acknowledgments, this is what Dan Brown wrote:
FACT:
The Priory of Sion — a European secret society founded in 1099 — is a real organization.
In 1975 Paris’s Bibliothèque Nationale discovered parchments known as Les Dossiers Secrets, identifying numerous members of the Priory of Sion, including Sir Isaac Newton, Botticelli, Victor Hugo and Leonardo da Vinci.
The Vatican prelature known as Opus Dei is a deeply devout Catholic sect that has been the topic of recent controversy due to reports of brainwashing, coercion and a dangerous practice known as “corporal mortification.” Opus Dei has just completed construction of a $47 million World Headquarters at 243 Lexington Avenue in New York City.
All descriptions of artwork, architecture, documents and secret rituals in this novel are accurate.
But these "facts" are, in fact, lies, as a previous post demonstrates. The book's intent is clearly defamatory, especially of Opus Dei.
Well, I haven't read the book and don't plan to and I won't be seeing the movie.