A bomb that detonated just half a mile away from Buckingham Palace is to be the subject of a new film produced by a group of British Army veterans.
Just after 10.30am on 20 July 1982, IRA terrorists exploded a device in Hyde Park at the precise moment 15 soldiers and horses from the Blues and Royals were passing by on their way to mount guard.
Four men and seven horses were killed, and many more were injured in the attack which sent shockwaves around the world.
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Forty years on, survivors of the Hyde Park bombing are telling their stories on film for the first time – readers may find some of the details of the attack upsetting.
Steve Sullivan is one of those men. Describing the terrible events that day, he said: "I never forget the feeling when that bomb went off.
"It was like having every little bit of oxygen drawn out of your body.
"I don't know if you have ever fainted. It's that feeling you get just before you pass out.
"And it's an emptiness. It just sucks the life out of you.
"Awful feeling. Horrible," he added.
The victims of the bombing were members of the Blues and Royals, part of the Household Cavalry Mounted Regiment.
In their state ceremonial uniforms, they were on their way to the Changing of the Guard, a ceremony that goes back centuries and one that continues today.
Andrew Parker Bowles was the commanding officer at the time. He defines the bombing as the "saddest moment" of his military career.
"I sort of worked myself up into quite a thing," the retired brigadier said.
"Could I have done something better? Should we have done something better?"
When the bomb went off, nails and shrapnel sprayed the men and their horses, causing death and significant injuries.
Yet, out of the tragedy, one of the most inspiring survival stories in modern history emerged, that of the world-famous cavalry horse Sefton.
The filmmaker behind the project, Mauricio Gris, himself a former captain in the Household Cavalry, said he intended the film to focus on the men who walked away with their lives.
He said: "At the time, the horses were the focus of the story, so I wanted to capture the human side of this tragedy and also explore what it means to the people involved 40 years on.
"I couldn't believe their story hadn't been told before."
Mauricio is leading a team of professional filmmakers, made up of fellow Army veterans, to produce the film on the 40th anniversary of the deadly attack.
But the project requires finance, so they have launched a crowdfunding page and are calling for people to support their work with donations.
Every day, as the on-going and off-coming guards ride past, members of the Household Cavalry salute the spot where, four decades earlier, their colleagues lost their lives, and life changed forever for those in the regiment going on public duties in the capital.
Speaking ahead of appearing in the film, Steve Sullivan said that his memory of the attack "still hurts".
"There's not been one day of my life since that day that I haven't remembered something that went on.
"It's always, always been part of my life ever since," he added.
There are rewards available for those able to contribute to the film, including a behind-the-scenes Champagne tour of the Household Cavalry Museum at Horse Guards in London.
Anyone who would like to make a donation can visit the team's crowdfunding page here.