TIM KNATCHBULL was just a boy on a holiday fishing jaunt in Ireland, but it turned into one of the most high-profile terrorist attacks of all time.

The murder of Lord Mountbatten of Burma, members of his family and teenager Paul Maxwell by the IRA off the Irish coast, left Britain reeling.

It occurred just 15 minutes after Donegal fishing boat Shadow V had left a small County Sligo harbour.

Watching the happy party through binoculars had been a hidden terrorist who, at exactly 11.45am on August 27, 1979, pressed the button, exploding the 50 pounds of gelignite stashed beneath the fishing boat.

It blew the tiny vessel to pieces.

Prince Charles's great uncle and godfather Lord Mountbatten, one of his grandsons, Nicholas Knatchbull, and 15-year-old ship-hand Paul Maxwell, were all killed immediately.

Although initially thought to be only slightly injured, The Dowager Lady Brabourne, 83, died the next day in hospital.

Now the cold-blooded atrocity - and its aftermath - is to be the subject of a book and television programme created by one of the central characters in the tragedy who, until now, has never spoken publicly about what happened.

Today, Timothy Knatchbull lives in America, where he has a career as a documentary film-maker for the Discovery Channel.

In the summer of 1979, he was a 14-year-old schoolboy, growing up safe in the knowledge that his identical twin brother and confidant Nicholas would travel through life with him.

How wrong he was.

The blast, which killed Nicky instantly, left Tim floating unconscious and seriously injured, deafened, his eyes scorched and his lungs filling with blood.

Plucked from the sea, his battered body was rushed to Sligo Hospital where he lay near his parents, Lord and Lady Brabourne, who were both seriously injured, too.

Later, the news was broken to him that his twin had not survived.

Unveiling plans for his book about the events which decimated his family, Tim told The Mail on Sunday: "I couldn't believe that I could be alive and he could be dead.

"It was a flashpoint in my life. I knew I was either going to be injured forever, limping and lame, or I was going to get through it.

"I was determined to survive because of the 14 years Nicky and I had shared together, where he had been this incredible soulmate."

Tim's mother, Lady Brabourne - now Countess Mountbatten of Burma - has said the last thing she recalls before the explosion was her mother-in-law exclaiming what a lovely day it was.

Then, in the split second following the blast, she thought the fishing boat's diesel engine had blown up.

"I came round under the water, going round and round," she said.

"I remember floating around with some bits of wood, which I had no idea were the boat. I was fearful of coming up under the upturned boat, but there was no boat to be trapped under.

"I was aware there must be a lot of injuries to my face, and I was going in and out of consciousness."

Lady Brabourne was the first victim to be rescued by shocked onlookers manning the 12ft dinghy, who later discovered her father's body, identifiable by its distinctive jersey.

She and her husband spent weeks in hospital recovering from their injuries.

Then, in incredible acts of personal bravery, they both attended the wedding of their eldest son, Norton, in wheelchairs just two months after the attack.

"You just have to get back into the swing of things as soon as you can," she explained.

Now Countess Mountbatten carries "a large measure of sorrow", which she knows will be with her to the end of her days.

In the aftermath of the atrocity, one of her concerns was that people's memories of Nicky's short life might fade.

She is comforted by the fact that his name lives on in an NSPCC trust fund, set up by his six brothers and sister, which provides holidays for both Protestant and Catholic children in Ireland who might otherwise not mix.

His old school, The Dragon, in Oxfordshire, also has a fund in his memory, which helps fund gap year voluntary work and expeditions for pupils.

And so, over the years, the Mountbatten family has gone about slowly, and painfully, rebuilding their lives.

Amazingly, five months after his grandfather's murder, Tim went back to school and went on to gain an economics degree from Cambridge.

In 1987, he returned to Mullaghmore, the place where his life was turned on its head that hot and balmy August Bank Holiday Monday.

Eight years later, at the age of 30, he finally sought the help of a bereavement counsellor, as a result of which he no longer regularly hears the sound of the bombing ringing in his ears.

In 1998, Tim married teacher Isabella Norman at Winchester Cathedral, at a ceremony attended by the Queen, Prince Philip, Prince Charles and Princess Margaret.

The couple honeymooned in Ireland.

Which brings us to probably the most amazing part of this story - that is, the way the Mountbatten family refuses to bear a grudge about what has happened and still hopes for a solution to Ireland's political problems.

Within days of the bombing, Lord and Lady Brabourne strongly asserted that they felt the Irish were their friends.

"The most important message is that I have no bitterness, none whatsoever. It has allowed me to grow and to lead a happy and fulfilled life," Tim told The Mail on Sunday.

"Exploring it will be rewarding, challenging, difficult and painful but it is going to be positive."

Before the terrorist attack, the Mountbattens had holidayed at Classiebawn Castle for many years.

It was a place of family love, laughter and relaxation.

On arriving on the ferry in Dublin in the summer of 1979, Lord Mountbatten was met by the British Ambassador to Ireland to be told of intelligence reports anticipating a forthcoming attack.

Despite his close connections with royalty, he honestly didn't believe terrorists would want to kill an old man.

Lord Mountbatten accepted four armed guards from the Irish Special Branch - but refused to change his plans and then spent most of his time trying to give them the slip.

Just the night before the bombing, he was joking about people enjoying themselves at his funeral.

To the Provisional IRA, he was the perfect target - Prince Philip's uncle, an Admiral of the Fleet, former Viceroy of India and a Second World War hero who had survived having a ship blown up beneath him.

Tragically, Lord Mountbatten had no chance of surviving this second attack.

Eventually, Thomas McMahon, the man who planted the gelignite on Shadow V, received a life sentence for murder.

Yet on the evening of August 6, 1998, the 50-year-old walked free from Dublin's Mountjoy Prison as part of the Good Friday Agreement after serving 19 years behind bars.

That Tim Knatchbull is embarking on what will probably be the most crucial emotional journey of his life in such a public way, is inspirational to us all.

And a fine example to everyone involved in the peace process today.