In 1967, Belgian diver and treasure hunter Robert St£nuit discovered a Spanish Armada warship that sank on Antrim's north coast nearly 400 years before. In secret, the Belgian began to excavate the wreck and carefully recover what would become a fortune in Spanish gold.
When the Press was alerted to what was going on, the story instantly captured the public's imagination.
It gave Antrim's north coast an archaeological site of world importance and re-wrote the Armada story.
The ship was the Girona and its enormous hoard of gold meant Robert's life would never be the same.
As a young boy, Portballintrae had been my playground. I'd spent every summer camping with my grandmother in the little boathouse at the top of the village slipway.
I actually witnessed Robert, dressed in his frogman's gear struggling with his frogmen companions, to haul an ancient cannon onto Portballintrae harbour.
The fertile imagination of youth has made this man my own real-life Indiana Jones.
Now, 40 years on I was flying to Brussels with a bottle of locally produced whiskey. I hoped it would rekindle Robert's own memories of Portballintrae.
It had taken months to contact this man who still travelled the world looking for sunken treasure ships.
Now in his 70s, I planned to persuade Robert to make one final dive on the Girona site: the wreck that had made him famous.
He was happy to talk about how he found and recovered the Girona's treasure.
Would, I wondered, the enigmatic Belgian finally reveal how it felt to discover the most important collection of Armada artefacts the world now has.
Persuading him to re-tell his story turned out to be an 18-month-long battle of wills between us.
Port na Spaniagh, one headland away from the Giant's Causeway, is undoubtedly an epic location.
It was here on a wild October night in 1588 that the Girona was ripped apart on razor sharp reefs. Nearly 1,300 desperate and terrified Spaniards drowned in a cauldron of writhing surf, trapped beneath towering cliffs.
Robert Sténuit eloquently describes Port na Spaniagh as a place designed for destruction and death: a setting that could have been made by Hollywood for a film on shipwreck.
Robert could also be a character straight out of the movies.
He is a diving legend, who still boasts that he's never held a diving licence — a true maverick in the exciting and dangerous world of international wreck hunting.
People in Portballintrae vividly remember him as an elegant and sophisticated foreigner, who raced around the north coast in a little sports car.
In the summer of 1967, just as Northern Ireland was about to begin its descent into violence, Robert brought a whiff of adventure with tales of sunken treasure.
For me the key to making this film was to get Robert to reveal something he's never done before; the thrill and joy of finding that first elusive piece of Armada Gold. Robert has spent 40 years carefully keeping this side of his character under wraps.
He has portrayed himself as an academic and historian, carefully guarding his reputation and keeping his emotions under tight control. Robert would prefer to be remembered less as a treasure hunter and more as a pioneering underwater archaeologist.
For 400 years the Girona's treasure has overshadowed her doomed crew.
From the dark October night, when she was wrecked on the Antrim rocks, people coveted the gold that fell from the pockets and slipped from the fingers of her drowning men, their lives not worth knowing and quickly forgotten.
It was their deaths that lured Robert Sténuit to Port na Spaniagh. Yes, he did come to find their gold, but with each precious piece he prised from the sea bed he also uncovered a long-forgotten story.
Slowly he came to see those unfortunate souls for the men they had been.
He learned of their wealth and power. He understood their faith and felt their fears and superstitions.
He found precious reminders of loved ones left in Spain. These were men who had travelled the world before being lost on the edge of Ireland and Robert spent three summers diving for more of the treasure that had been theirs.
Robert Sténuit was a tough nut to open. After talking to him on camera no fewer than a dozen times, I believe both sides of this complex man and his compelling story are finally there to be seen.
It was gold that lured him to Port na Spaniagh; it was gold that gripped our imaginations and it was the Girona gold that pushed Northern Ireland's Troubles off the world's headlines for a few short weeks.
Sténuit, along with his colleague Marc Jasinski, a pioneering underwater film-maker, returned to Port na Spaniagh, now Ireland's first protected wreck site, where they were given special permission to dive and explore the spot they made famous one more time.
Now safely stored in the Ulster Museum, Robert's golden hoard has been saved for everyone to see.
Yet Robert insists that gold is not the only treasure.
He argues that without the stories he uncovered these treasures are just precious trinkets.
It's the stories they tell and the understanding they can still give that are the Girona's real and enduring treasure.
The Great Girona Gold Hunt is presented by Neil Oliver (from BBC2's Coast series) on BBC1 NI, tonight at 9pm