LEE HARVEY OSWALD did NOT act alone – and The ENQUIRER can finally name the second gunman who fired the fatal shot at President JOHN F. KENNEDY from the grassy knoll in Dallas 50 years ago!

In a blockbuster exclusive, The ENQUIRER has learned that a Cuban exile with ties to both the Mafia and the CIA confessed to being involved in a conspiracy to kill America’s beloved 35th president.

The startling new evidence was uncovered by re­spected author Anthony Summers, who revealed the assassin’s identity in an update to his classic 1998 book on Kennedy’s slaying, “Not In Your Lifetime.”

According to Summers, the second rifleman was Herminio Diaz, a hired killer who worked for notorious Mafia boss Santo Trafficante Jr. in Cuba. Diaz executed a Cuban police chief in the late 1940s and likely committed 20 murders in his lifetime.

“Lee Harvey Oswald did not act alone,” Summers told The ENQUIRER.

“There was a conspiracy to kill President Kennedy, and the same people who hired Lee Harvey Oswald – whether it was the CIA, the Mafia or Cubans opposed to Fidel Castro – also hired Herminio Diaz.”

Diaz arrived in the U.S. in mid-1963, according to CIA documents, just months be­fore Kennedy was struck down in Dealey Plaza on Nov. 22 of that year.

“Diaz was a professional hit man with a record of political assassina­tions,” Summers said.

“He’d also worked for Mafia chief Trafficante as security director of the Hotel Habana Riviera casino in Cuba.

“He was in the country at the right time and was involved in the anti-Castro movement. Many people in that movement thought President Kennedy had betrayed them during the CIA-sponsored Bay of Pigs invasion in 1961 and the Cuban Missile Crisis in 1962, and had a motive to kill him.

“Frankly, it all adds up.”

According to Summers, Diaz revealed his role in the Kennedy assassination to a friend named Tony Cuesta. The two men were headed to Cuba by boat on an anti-Castro raid in 1966 when Diaz spilled the details on the murder plot.

“Diaz and Cuesta talked on the boat while waiting to land in Cuba,” Summers said.

“During their conversations, Diaz admitted to Cuesta that he’d taken part in Kennedy’s death.”

Diaz was killed in the raid. Afterward, a photo published in a Cuban Communist Party newspaper showed that he was carrying a valid Florida driver’s license and a Social Security card when he died, evidence that he had indeed been in the U.S.

His buddy Cuesta was badly injured in the raid, captured and jailed at Cuba’s infamous La Cabana Prison. While being treated at the jail infirmary, Cuesta confided Diaz’s assassination story to another anti-Castro inmate, Cuban Rein­aldo Martinez. After his release from prison, Martinez fled to Miami, and in 2007 he contacted G. Robert Blakey, who’d served as chief counsel of the U.S. House Select Committee on Assassinations.

“Martinez thought he was about to die and wanted to set the record straight,” Blakey told The ENQUIRER.

“After speaking with him, I believe he was telling the truth. It wasn’t just Lee Harvey Oswald who killed Kennedy. It was a conspiracy, and Herminio Diaz was the second shooter.”

Summers also interviewed Martinez for two days in Miami.

 “Martinez had nothing to gain by telling his story, except for setting the record straight,” Summers, who videotaped the interview, told The ENQUIRER.

“He told me he was close to death and was telling the story because, ‘It is the truth – my truth.’”

Kennedy’s brutal slaughter stunned America and prompted his successor, President Lyndon B. Johnson, to order a thorough investigation of the tragedy. According to the official Warren Commission report on the assassination, Oswald acted alone in shooting Kennedy.

BUT in the famed Zapruder film that shows the presidential motorcade moving through Dealey Plaza, Kennedy is first hit from behind, where Oswald was located in the Texas School Book Depository.

After that, it appears that Kennedy was hit from the front at an angle which would indicate a shooter located on the “grassy knoll.”

One expert who’s convinced there was a second shooter is world famous medical examiner Cyril H. Wecht, who’s spent decades studying the assassination.

“Based on the available medical, physical and photographic evidence, all of which I’ve exam­ined multiple times, the assassination of President John F. Kennedy was carried out by two gunmen – not just Lee Harvey Oswald,” Wecht told The ENQUIRER. According to his analysis, Wecht says two gunmen fired four shots, and one assassin was situated at the front of the motorcade.

“Based on the initial backward trajectory of the president’s head after being impacted by the gunshot blasts, I believe a shooter operated from the right front of the vehicle behind the picket fence on the grassy knoll,” he said.

“Eyewitness accounts corroborate this.”

While the Warren Report discounted that scenario, multiple eyewitnesses told the same story to the congressional committee between 1977 and 1979, according to Blakey.

“At our hearings, there was lots of testimony that a shot was fired from the grassy knoll,” Blakey, also author of the anti-mob RICO act and professor emeritus of law at Notre Dame, told The ENQUIRER.

“I believe there were four shots. The first, second and fourth shots came from the Texas School Book Depository. The third shot came from the grassy knoll.

“The committee had everything but the names of the people involved in the conspiracy. Marti­nez’s story has filled in the last pieces of the puzzle. There were two shooters.”

According to both Summers and Blakey, Marti­nez approached the FBI to tell his story but was told that the assassination investigation was closed.

And Blakey called Summers’ discovery of Diaz’s role in the assassination a “breakthrough of historical importance.”

“Summers’ book deserves to be read and taken seriously by all those who care about truth or justice,” he said.

Summers added: “I completely believe the stories told by Reinaldo Martinez and Tony Cuesta about Herminio Diaz’s role in the assassination of President Kennedy.

“Fifty years after the fact, their information has blown the investigation into the Kennedy assassi­nation wide open!”