NOW IT CAN BE TOLD! Mass-murder mastermind CHARLES MANSON was set on fire by vicious prisoner, who boasted he’d kill the “Helter Skelter” madman!

And convicted killer Jan Homstrom nearly made good his threat –igniting the infamous cult leader.

 “Manson survived, but he could have easily been killed!” says a now-retired corrections officer who was one of the first guards at the scene of the 1984 assassination attempt.

Few details of the horrific incident have ever been released, but the source says Manson’s skin actually melted, and he was just a heartbeat away from death after being turned into a human torch.

Caged for life for inciting the 1969 “Helter Skelter” rampage slayings of actress Sharon Tate and eight others, Manson conducted a reign of terror in prison in the years after his January 1971 convictions, say sources.

Guards documented his assaults on other inmates, knowing trouble was brewing and the prison’s law of the jungle decreed Manson was due for payback.

The 5-foot-7 icon of evil met his match when he made the mistake of bullying Holmstrom, another “psychiatric inmate” who stood almost a foot taller. The bearded giant was doing time for brutally murdering his father.

At 8:18 a.m. on Sept. 25, 1984, while both were in the hobby shop of the California Medical Facility, Holmstrom pounced, dousing Manson with a cup of paint thinner, lighting a match and gleefully watching him burn. A prison instructor raced to Manson’s rescue – and frantically tried to douse the flames.

The ex-guard said he was in the prison “watch office” when a loud siren went off signaling a cellblock incident was underway.He and several officers raced to the hobby shop and saw Manson, with a wet towel covering his face, being helped toward a doorway by the instructor.

“He was screaming, ‘My face is burned!’ ”said the source. “Manson was lucky because it turned out that his beard prevented much more serious injury.”

The source says Holmstrom hid the flammable liquid in a cup and pretended to drink it until he was next to his target. The source says, “Manson didn’t stand a chance.”

Manson, then 49, suffered second- and  third-degree burns to 18 percent of his body – mostly his face, scalp and hands – in the attack. The skin on his forehead was melted by the flames, the source says.

But Manson eventually made a full recovery and was returned to his maximum security cell at the Vacaville prison, 50 miles north of San Francisco.

Photographic evidence of Manson’s disfiguring burns was snapped by correction officials the attack and placed in a file. But the dossier never saw the light of day because an attempted murder case against Holmstrom never got off the ground, the source explained.

Holmstrom, then 36, was only charged with assault. At a hearing four months later, that  case evaporated, too. In view of Manson’s attacks on other inmates, officials determined a conviction would be unlikely because Holmstrom acted in self-defense.

A parole board eventually freed Holmstrom in 1990, despite pleas from his terror-stricken family to keep him caged. Holmstrom tried to kill another man four years later. Found not guilty by reason of insanity, he was hauled off to a high security psychiatric facility.

Manson, 78, remains behind bars at Corcoran State Prison and has been denied parole 12 times.