The Priory of Sion really did exist. In one sense this is true; it even published a periodical in the 1950s and 1960s. Unfortunately, it doesn't appear to predate 1956. See the first item under "False" below.
The BBC aired a series of documentaries giving credence to the stories about the French town of Rennes-le-Château and its connection with the Priory of Sion. True. In 1997, however, the BBC produced another documentary admitting the story wasn't true.
The medieval Knights Templar were particularly close to the pope. In 1139, Pope Innocent II declared that they would be answerable only to the papacy.
The Knights Templar were very rich. It was part of their Rule that all new members had to hand over their property to the order.
Friday the Thirteenth is unlucky because the attempt to exterminate the Knights Templar took place on Friday, Oct. 13, 1307. This is one possible explanation, although it has a lot of competition.
The Priory of Sion preserved the truth about Jesus and Mary Magdalene for centuries. Sorry. Documents related to the history of the Priory of Sion were proved in the 1990s to be an elaborate hoax.
Isaac Newton, Botticelli, Victor Hugo and da Vinci all belonged to the Priory. Well, if the Priory was a hoax, this wouldn't be true either, would it? Jean Cocteau was another nonmember, although it's intriguing to think of the author of Les Enfants Terribles entrusted with weighty religious secrets.
The Bibliothèque Nationale in Paris contains documents that prove the Priory really did exist. These were planted by a hoaxer with the remarkably appropriate name of Pierre Plantard.
An early Grail romance suggests the sacred chalice was guarded by the Templars. Not in any accepted interpretation.
The Merovingian kings of France were descended from Jesus and Mary Magdalene. Quite a stretch. Although Dagobert II was indeed murdered, as Leigh Teabing states, historians do not see the hand of the Vatican behind the fatal dagger.