Richard Leigh and Michael Baigent are suing Brown and publisher Random House in London's High Court, claiming "The Da Vinci Code" usurped their book "The Holy Blood and The Holy Grail," the BBC reported.
"I have been shocked at their reaction. Furthermore I do not really understand it," Brown said in a statement Monday.
"I would like to restate that I remain astounded by the claimants' choice to file this plagiarism suit," he said. "For them to suggest, as I understand they do, that I have hijacked and exploited their work is simply untrue."
Both books are centered on a theme that Jesus survived crucifixion and had children with Mary Magdalene.