Author Dan Brown has dismissed accusations that he stole the ideas for his best-selling novel The Da Vinci Code as "completely fanciful".
Dan Brown's The Da Vinci Code has sold 40 million copies worldwide
The novelist is appearing at London's High Court after historians Richard Leigh and Michael Baigent sued publisher Random House.
They say Mr Brown copied ideas in their book The Holy Blood and The Holy Grail.
"I have been shocked at their reaction. Furthermore I do not really understand it," Mr Brown said in a statement.
Both books explore a theory that Jesus did not die on the cross but survived and had children with Mary Magdalene, and that their descendents survive.
Mr Brown said Mr Baigent and Mr Leigh were just two of a number of authors who had written about the theory.
"Yet I went out of my way to mention them for being the ones who brought the theory to mainstream attention," his statement said.
"I would like to restate that I remain astounded by the claimants' choice to file this plagiarism suit.
"For them to suggest, as I understand they do, that I have hijacked and exploited their work is simply untrue."
Mr Brown told the court his wife Blythe carried out much of the research and she "was deeply passionate about the sacred feminine".
He said it was hard to pinpoint the sources he and his wife used while researching The Da Vinci Code.
"On the way, we met with historians and other academics and extended our travels from the Vatican and France to England and Scotland in order to investigate the historical underpinnings of the novel," he said.
He was originally unsure whether to include the theory that Jesus' bloodline had survived because he thought readers would find it "too incredible and inaccessible", he said.
But his wife persuaded him and he said he was "positive" he read about it in many sources before reading The Holy Blood and The Holy Grail.
The author grew up on the campus of Phillips Exeter Academy, New Hampshire, where his father was a teacher and where he studied.
Code of conduct
"It is also known for the strictness of its regulations and code of conduct, especially with respect to plagiarism," he told the court.
Mr Baigent previously told the High Court Mr Brown stole "the whole architecture" of research that went into their book.
He said there were "fairly specific" similarities between the books, but conceded there were many differences.
Random House has said Mr Brown used several sources for his research and wrote a synopsis of The Da Vinci Code before even looking at The Holy Blood and the Holy Grail.
The Holy Blood and the Holy Grail's third author, Henry Lincoln, is not taking part due to ill health.