Twenty years ago The Da Vinci Code gripped the world with the notion that Jesus Christ married, had a secret honeymoon in France and sired a hidden line of future European rulers. You probably know the story. After all – Dan Brown’s conspiracy thriller sold 80 million copies within five years of its release and spawned a film franchise.

But the story you may not know is that key parts of the theory have their origins not in the archives of The Vatican, but in the vaults of the BBC. Kevin Core, producer of Seriously’s Archive on 4: The Holy Blood, tells us the story of the fraud that sparked a conspiracy movement.