More than 50 years after President John F. Kennedy was gunned down in Dallas, new evidence uncovered in the secret diaries of a Cold War spy and assassin implicates another clandestine figure believed to be working as a double agent for Cuba, an explosive new book claims.

The never-before-revealed diaries of Douglas DeWitt Bazata, a decorated officer for the United States Office of Strategic Services — the forerunner of the Central Intelligence Agency — claim that his longtime close friend and fellow spy, René Alexander Dussaq, was a “primary organizer and plotter” of Kennedy’s assassination on Nov. 22, 1963.

The diaries reveal that Dussaq might even have fired the fatal “shot or shots” that killed the 35th president of the United States, according to author Robert K. Wilcox’s latest book, “Target: JFK, The Spy Who Killed Kennedy?,” which goes on sale Nov. 14.

“Douglas Bazata was deeply embedded in the world of secrets, especially those surrounding JFK’s death,” Wilcox writes. “He was there at the birth of the CIA as an early and major player in that murkiest of worlds … He was an insider.”

In his diaries, Bazata wrote that the two men first met in Havana, Cuba, during the early 1930s, when Bazata, a US Marine, was given his first mission as a hitman: to assassinate a Cuban revolutionary. The mission failed, but the pair’s bond was sealed forever after Dussaq saved Bazata’s life.

The bond deepened in 1944, when both men were part of WWII’s Operation Jedburgh, in which more than 250 American and Allied paratroopers jumped behind enemy lines across France, the Netherlands and Belgium to fight against German occupation. Dussaq’s larger-than-life legend began here: He was nicknamed “Captain Bazooka” for demonstrating the Army’s new anti-tank rocket launchers to the Maquis, French resistance guerrillas. He’s also credited with bluffing a German general into believing he was surrounded by American troops, leading to the capture of up to 500 Nazis.

Dussaq — who was born in Buenos Aires and educated in Geneva and Cuba — became a naturalized US citizen in 1942. The son of a Cuban diplomat, he had tried to enlist after the Japanese attacked Pearl Harbor but was deemed a potential security risk. However, the US Army was desperate for infantrymen at the time and ultimately accepted him. Dussaq quickly rose through the ranks, becoming a lieutenant instructor for the elite 101st Airborne Division, the “Screaming Eagles.”

One top-ranked OSS official told his counterparts in London that Dussaq, who spoke six languages, was an exceptional athlete and a master of “unusual and hazardous work of a physical nature,” references to earlier work as a deep-sea diver, treasure hunter and Hollywood movie stuntman.

“He is keen, adaptable … intelligent … and a dirty fighter conversant with jujitsu and the commando type of close combat fighting,” the OSS official wrote. “ … Waldo Logan [of Chicago’s Adventurer’s Club and backer of some of Dussaq’s earlier seaborne expeditions] says that he is the only man he has ever known who is entirely without fear.”

Following the war, Bazata became a world-class spy and underground operative working for the CIA and other intelligence agencies. Dussaq, meanwhile, took a job as a Prudential insurance agent in Los Angeles. Within two years, according to Freedom of Information Act requests, he began infiltrating community groups in Hollywood and Mexico, if not elsewhere, on behalf of the FBI, Wilcox writes. Around this time, Dussaq, according to Bazata’s diaries, grew increasingly angry with the United States’ dominance and exploitation of Cuba.

Dussaq, according to Bazata’s diaries, launched the assassination plot to make a point to America about its leaders’ manipulation of smaller countries. Bazata was designated his historian.

“He delegated Bazata, when the time was right — after the assassination’s shock had dissipated — to tell the public the truth about what happened in hopes America’s leaders would change and allow sovereign nations like Cuba to decide their own fate rather than have America decide it for them,” Wilcox writes.

The CIA-sponsored Bay of Pigs invasion in 1961 and continued attempts by Kennedy’s administration to kill Fidel Castro finally prompted Dussaq to put his sinister “Hydra-K” assassination plot into motion, according to Bazata’s diaries.

“[Cuba] could not determine its own destiny and this was so big with Dussaq,” Wilcox told The Post. “He was a guy who believed that every person should determine their own destiny and every country should do the same.”

Wilcox told The Post he believes the coded diaries that Bazata gave him in 1999 prior to his death — several thousand handwritten pages in all — clearly indicate Dussaq was a double agent working for Cuba. In fact, Bazata writes that one of the reasons the Bay of Pigs invasion failed was because Dussaq was informing Cuba all along. Dussaq’s second wife, Charlotte, also told Wilcox that Dussaq was asked by the CIA to help plan the operation, but he declined.

Bazata and Dussaq would later begin plotting and rehearsing Kennedy’s assassination at meetings in the United States and Europe, including at the upscale Tremoille Hotel in Paris, where Bazata told Dussaq about his failed attempts to get US officials to take his warnings about the impending execution seriously. Wilcox’s book contains a memo he found among Bazata’s secret papers indicating that he and legendary CIA spy Lucien Conein discussed “Operation Hydra-K” long before the assassination.

“This Hydra-K document is hard evidence of what Bazata alleges,” Wilcox writes. “There is very little other ‘outside’ documentation that supports his story — although one can argue lack of documentation would be expected in such a secret and monumental conspiracy.”

Dallas was selected as the location for the assassination “as far back as 1961,” according to Bazata, since it was an anti-Kennedy “hothouse for murder” with one of the most corrupt police departments in the country.

Dussaq “ordered five triggers” for the assassination, with a second commander-manager (COs) standing behind each gunman, according to Bazata’s diaries. And if anything went wrong, each CO had a “cyanide inflictor,” unavailable even to the CIA at the time, that would kill instantly.

The shooters included Dussaq, Lee Harvey Oswald, an assassin code-named “Piatogorsky” and two unidentified CIA hitmen. Bazata’s diaries also cite other fringe players in the plot, including backup shooters, five body doubles for Oswald and random “pointers” and “shouters” designed to confuse police and witnesses.

“On November 22, 1963, half past high noon, Hydra-K commenced,” Wilcox writes. “As the motorcade approached, René, preparing to shoot, readied his weapon. Bazata doesn’t say where he is, only that he was a ‘great distance’ from his target. He is ‘in front’ of the motorcade. His soon-to-be-fired shot, however, would not be the first. It would be the second.”

Oswald, according to the Warren Commission, “acted alone.” The United States House of Representatives Select Committee on Assassinations (HSCA) later found a “high probability” that two gunmen fired at Kennedy.

But according to Bazata’s account, Oswald fired the first shot from above and behind Kennedy’s lurching motorcade. Wilcox notes that Bazata’s account then “deviates from the standard,” adding that Dussaq didn’t trust or want to include Oswald, the “unstable” former Marine.

“He was, after all, tabbed to be the patsy,” Wilcox writes. “Dussaq surreptitiously had Oswald’s rifle armed with duds, blanks, which Oswald would fire harmlessly at Kennedy. This ploy, this ‘red herring,’ Dussaq believed, would later be discovered and serve to exonerate the patsy and undermine and thus misdirect all ‘official’ investigations, clearing a path for Bazata’s subsequent planned revelations.”

Oswald’s CO, according to Bazata’s diaries, secretly inserted the dummy cartridges but Oswald “instinctively” realized something was off after firing the first shot: the signal that the execution was under way. Oswald then intentionally let a “clip” fall from his rifle and inserted a real cartridge into the gun and fired a second, authentic shot before the CO wrestled it away.

Oswald’s first dummy shot, as planned, distracted the droves of onlookers in Dealey Plaza. That allowed Dussaq, a “superb shot,” to fire the first lethal shot from his undisclosed location in front of the motorcade.

At nearly the same time Dussaq fired, another shooter identified only as a CIA operative fired from the rear, just as Oswald had done seconds earlier. The unidentified assassin and Dussaq were essentially aiming for the “exact same hole” and the third shot was “slightly higher in the head,” Bazata wrote.

According to Bazata, four shots were fired in all, including Oswald’s dummy. All shooters wore gloves and face coverings to protect their skin from powder debris, and their weapons and incriminating evidence were removed by “experts” as a squad extracted all involved. Dussaq left Dallas shortly afterward and fled to Mexico by private boat, while the others stayed behind with “solid cover-reasons” to be there.

‘You either believe me or you don’t. I care not one fig either way. I merely set down here a story 50 years in the making. It is all totally true.’ - Douglas Bazata

Bazata, for his part, says he was in Europe when Kennedy was killed. Wilcox acknowledges that means Bazata’s description of the assassination — if true — is second-hand in nature at best, most likely coming from Dussaq himself.

To protect his friend, Bazata referred to Dussaq throughout his diaries as “Peter” or, more often, “Paul,” a play on the biblical transformation of Saul to Paul. But he occasionally slipped and identified Dussaq outright, Wilcox said.

“Long have I kept Paul’s story in my heart,” one of Bazata’s diaries read. “Paul never spoke to me from bragging or compulsion. He spoke in tears and hope … He chose me to [tell the story] … You either believe me or you don’t. I care not one fig either way. I merely set down here a story 50 years in the making. It is all totally true … I change only the names of those I love [Dussaq and other clandestine brothers involved] and those I fear.”

Although Bazata’s diaries do not include, according to Wilcox, a “smoking gun” or a direct link to Castro, they point to Dussaq being the “mastermind” behind the assassination who led the operation in Dallas. Dussaq referred to Castro as “boss” at one point in planning, according to Bazata.

“There are only four scenarios: It was the rogue CIA, it was Cuba, it was Russia or it was the Mafia,” Wilcox told The Post. “Or, it’s a combination of all of those and my book fits into that because the real finger is pointed toward Castro and Cuba, but there are CIA players and Mafia involved.”

Wilcox said Bazata gave him the diaries during a series of interviews for his 2008 book on Gen. George Patton at Bazata’s home just before his death at the age of 88.

“He never would’ve given them to me at the time unless he had a stroke,” Wilcox said. “All of his defenses were down. I found these down in his basement and I said, ‘Can I have these?’”

Upon realizing the monumental find he might have made in Bazata’s diaries, Wilcox tracked down Dussaq and realized he lived just miles away. Dussaq had died of cancer just three months earlier, but his second wife, Charlotte, gave Wilcox the spy’s “secret stuff,” including an unpublished autobiography that was crucial to the book.

In 1994, Dussaq was among a group of WWII veterans who re-enacted their invasion of German-held France 50 years earlier. At 83, he was the oldest of the bunch. Prior to the jump, Dussaq told The Post’s Kyle Smith from his home in Encino, Calif., that he was not a “worrying person.”

“Those of us who were paratroopers have a very strong feeling of oneness with each other,” Dussaq said. “And we have a very strong awareness of those who went with us and didn’t make it … We are doing it to commemorate those who were not lucky enough to survive it.”

As usual, nothing was simple or predictable for Dussaq, whose extraordinary life also included feats like walking on his hands atop the Empire State Building and witnessing one of the first atomic bomb tests on Bikini Atoll in the Marshall Islands.

Strong winds during the re-enactment jump blew Dussaq miles from the drop zone. He was later found in a nearby French town, drinking a glass of wine, the Los Angeles Times reported.

Dussaq told the Washington Post at the time that he had been “coming to pieces” of late, being treated for cancer, a collapsed lung, a hernia and asthma. Dussaq, who said he was “once a man of violence,” suggested to a reporter that maybe he was there to redeem his youth, before saying he found enough adventure of late by simply tending his garden.

“You know what they say: When the devil gets old, he retires to a monastery,” Dussaq said.

“Target: JFK, The Spy Who Killed Kennedy?” by Robert K. Wilcox will be available Nov. 14.