1982 "Holy Blood Holy Grail" by Michael Baigent, Richard Leigh, and Henry Lincoln

Before Dan Brown's fictional book the "DaVinci Code" came to the public eye. This was the book that shook the world since Charles Darwin's "Origin Of Species" was published in 1859. In The Holy Blood and the Holy Grail, the authors put forward a hypothesis, that the historical Jesus married Mary Magdalene, had one or more children, and that those children or their descendants emigrated to what is now southern France. Once there, they intermarried with the noble families that would eventually become the Merovingian dynasty, whose special claim to the throne of France is championed today by a secret society called the Priory of Sion. They concluded that the legendary Holy Grail is simultaneously the womb of saint Mary Magdalene and the sacred royal bloodline she gave birth to.