Da Vinci?s Last Supper and, (below) Tom Hanks who is set to play Robert Langdon

It became a publishing phenomenon in 2003 and raked up a roaring controversy. The Da Vinci Code eventually sold over 17 million copies in more than 40 languages around the world and filming has just begun on the $100-million movie adaptation, starring biggies like Tom Hanks and Alfred Molina.

But was the Code all fact or fiction? Was Jesus Christ married? Does his bloodline still exist? Author Dan Brown himself faces the camera to hold forth on all this and more in National Geographic Channel?s Unlocking Da Vinci?s Code: The Full Story, airing on Sunday.

Besides an exclusive interview with Brown, the documentary features opinions from clerics, art historians and some of the world?s leading authors on the topic, and raises more intriguing questions.

?The idea is not to stir up any controversy but make people think again on this subject, which is the motto of the channel,? said Rajesh Sheshadri, vice president (marketing), National Geographic Channel.

Dan Brown speaks candidly in the 90-minute special. On being asked if the underpinnings of the plot are accurate, he says the information has been around for a while, but in history tomes that sit in the back corner of bookstores. ?The Da Vinci Code has taken a lot of that information and put it forth in a different sort of genre, and an enormous portion of the population is hearing this for the first time now.?

Brown also says he started researching the book as a sceptic, trying to disprove the theory about Mary Magdalene, the person Jesus Christ supposedly married. But then, he ?became a believer?.

On Leonardo Da Vinci, the author says: ?There?s a great quote about Leonardo ? ?he was a man who awoke from a deep slumber only to find the rest of the world was still sleeping?. He was an alchemist, a mathematician, an architect, an inventor? a man really centuries ahead of his time. And he had the unfortunate challenge of being a modern man of reason born into an age of deep religious fervour? an age where science was synonymous with heresy.?

Da Vinci?s age and surroundings were responsible for the master painter hiding information in his works, like the Mona Lisa and The Last Supper, Brown adds. ?He was living at a time when you couldn?t just stand on a street corner and proclaim how you felt on a topic that was contrary to the church.?

The more he learned about Da Vinci, the more Brown began to sense that he would tell his story in a very secretive way.

On asked why some historians dismiss the theory that the figure to the right of Christ is that of a woman, Brown replies: ?I think it?s because we see what we?ve been told we see.?

?The fact that somebody as learned and advanced as Da Vinci would put Mary Magdalene at the centre of this incredibly important moment in history either implies that he did it tongue-in-cheek or that he knew some things that we didn?t.?

Brown also discusses the Knights Templar who supposedly protected the Holy Grail, the Roslyn Chapel in Scotland, which is supposed to hold clues to a secret, and other aspects of The Da Vinci Code.

Catch it on National Geographic Channel on July 3 at 10 pm.