The latter, having been (and indeed labeled as such, by the author) a work of fiction, it is not possible to "discredit" it. Perhaps what you meant to say was that some of the "theory" underlying the fictitious work has been discredited (ie, "Holy Blood, Holy Grail", and the Mary Magdalene as wife/consort of Christ, etc...)
the infowarrior
No, thank you, I meant exactly what I said about Dan Brown’s book. Labeling a book a novel does not mean the author does not pretend to offer any factual* content. Yes, it’s fiction, but Dan Brown and millions of his acolytes think that he provides accurate historical revisionism embedded in a fictional story. Look, he had a statement in the front which asserted that the book was completely factual about its treatment of art, religion, etc. He has millions and millions of people believing that he has offered a fictional story within a background of factual accuracy about Leonardo’s work, Mary Magdelene and a supposed “Holy Grail” etc. It certainly can be said that Brown offered all sorts of factual claims which as been discredited as either (1) obviously untrue, or (2) completely unsubstantiated in the historical record.
*I also maintain that one of the worst aspects of much fictional literature, even by some very good writers, is that it takes no responsibility for seriousness when it comes to treatments of historical matters. It’s too easy an out to say “well it’s just fiction” when an author has offered material that is obviously intended to be taken seriously as historically accurate, but it’s not.