They were eight seconds that changed the world - former marine Lee Harvey Oswald leaned out of the sixth-floor window and squeezed the trigger on his bolt-action rifle three times.

As a bullet blasted through John F Kennedy’s neck, hero secret service agent Clint Hill was the first to react, leaping out of a following car and racing towards the presidential limousine.

Mr Hill leapt on to the back of the accelerating car, trying to create a human shield to protect the president and his wife Jackie.

But he was seconds too late. Before Mr Hill could scramble into position, another shot pierced President Kennedy’s head, shattering his skull and showering blood and brain matter all over the car.

In an interview with The Sun on the 55th anniversary of the assassination today, Mr Hill, 86, reveals how he will never be able to forget the shocking and gruesome image of the president’s last moments.

And, tragically, even now Mr Hill still believes “he should have been faster” - and blames himself for the president’s death.

“One thing that I’ve never been able to erase from my mind is being on the back of the car looking down at the president, who was lying with his face in Mrs Kennedy’s lap,” Mr Hill said. “The right side of his face is up and I can see that his eyes are fixed. There’s blood everywhere.

“I can see the gunshot wound. In the room that’s in the skull I can see that there is no more brain matter left,” he said. “That is something I could never, and have never been able to, erase from my mind.”

“At the time I never thought ‘I might be killed’ or ‘I won’t see my kids again’,” Mr Hill said. “I didn’t think of that at all. That was the farthest thing from my mind. My goal was to get there to form a cover for them so no more damage could be done.”

“I think I should have been faster,” he said. “My job was to protect them and I was unable to do that.

“If I had been slightly faster I may have been able to prevent the president’s fatal wound and that has bothered me ever since. It always will - I’m sure.”

Mr Hill also revealed that the incident took a personal toll on him and he suffered post traumatic stress disorder and cut himself off from almost all friends and family and barely saw anyone other than his wife and two children from 1976 until 1982.

“I self medicated with alcohol during that period of time,” Clint admits. “I just didn’t care about anything and I didn’t want to have any contact with anybody.

“Friends would come by and I wouldn’t even acknowledge that they were there. I just ignored everything.”

Mr Hill said he made a choice to live back in 1982.

“I quit drinking, quit tobacco, started to work out a little bit. And I began to gradually get better and better,” he said. “And finally by 1990 I was able to go back to Dallas and walk the streets of Dealey Plaza up into the Texas School Book Depository and look up at the sixth floor window where Oswald shot from and then come away knowing that I had really done everything I could do that day.”

Mr Hill said the secret service today has a tougher job and that he would be concerned if he was guarding US President Donald Trump.

“The challenges are much greater to protect the president, whoever it might be,” he said. “And the fact that President Trump does generate a great deal of animosity from various sections of society, it is something that is very concerning.

MYSTERY OF JFK’S MISSING BRAIN ‘SOLVED’
Mr Hills comments came as it was reported that JFK’s missing brain was stolen by Robert Kennedy after his assassination to stop it ever going on display, according to secret US government files.

One of the greatest enigmas surrounding his death remains the location of his brain that mysteriously vanished.

The Sun reports that bombshell US Government documents actually back-up long-running claims that blame JFK’s younger brother RFK for swiping the brain.

Files compiled by the House Select Committee on Assassinations, which probed JFK’s murder, suggest the brain may have pinched to “prevent future display”.

The document reads: “Circumstantial evidence tends to show that Robert Kennedy either destroyed these materials or otherwise rendered them inaccessible”.

“It would seem to indicate that Robert Kennedy then decided to retain possession of all physical specimen evidence and transferred only the autopsy photographs and X-rays to the Government.”

The whereabouts of JFK’s brain have puzzled theorists for years after it was removed during the President’s autopsy and later disappeared from the National Archives.

Conspiracists claimed the missing organ vanished to conceal evidence that Kennedy was not shot from the back by Lee Harvey Oswald, but from the front.

A 2013 book called End of Days: The Assassination of John F. Kennedy, first claimed that an inquiry ordered by then attorney-general, Ramsey Clark, indicated that RFK was the thief.

The latest US government documents incredibly seem to agree with this theory, noting RFK wanted to keep hold of the brain to prevent “public display”.

US assistant Attorney-General Burke Marshall told the investigators: “Robert Kennedy obtained and disposed of these materials himself, without informing anyone else.”

The report states Marshall added: ““(He) was concerned that these materials would be placed on public display and wished to dispose of them to eliminate such a possibility.

“(He) emphasised that he does not believe anyone other than Robert Kennedy would have known what happened to the materials and is certain that obtaining or locating these materials is no longer possible.”

Robert Kennedy was killed on November 20, 1968, moments after winning the California primary in the race to become the Democratic candidate for the Presidency.

He was shot three times by Palestinian-born Sirhan Bishara Sirhan and died the following day after failing to regain consciousness.

The murders of both Kennedy brothers have been the subject of numerous conspiracy theories since their deaths.