O.J. SIMPSON has been slammed with a devas­tating diagnosis – his diabetes is a ticking time bomb that’s likely to go off within the next three months!

Doctors have diagnosed his condition to be so serious he could collapse in a diabetic coma or have a fatal heart attack at any time, says a pal of the disgraced 66-year-old football great.

To make matters worse, O.J.’s blood pressure is “sky-high” and he’s hastening his own death by refusing to take care of himself because he’s convinced he’s doomed to die behind bars.

“I know I’m gonna die soon,” a despondent O.J. told a close prison pal. “I don’t care anymore. My life is over. I’m done.”

Saying he has nothing to lose, the former gridiron hero has final­ly confessed to a pal that he killed his ex-wife Nicole and her friend Ron Goldman during an uncon­trollable fit of rage – and he plans to go out with a big bang by hav­ing his written murder confession released upon his death.

What’s more, The ENQUIRER has learned that Simpson devised a secret plan to assure that the $2 million he’s hidden away goes to his family and not to Ron Goldman’s relatives, who won a wrongful death lawsuit against him.

Meanwhile, O.J. has become bloated and sickly since being sen­tenced for up to 33 years in prison in 2008 after being convicted of kidnapping and armed robbery.

He reportedly tips the scales at a staggering 300 pounds and suffers from dangerously high blood pressure. And in recent days, his spirits plummeted as he became convinced the bid he’s making for a new trial would fail and he’d never again enjoy free­dom.

Severely depressed, he spends much of his time sleeping in his prison cell bunk at Lovelock Correctional Center in Nevada.

“O.J.’s doctors have told him he could be dead in as little as three months because of his out-of-control blood sugar and blood pressure,” revealed a friend.

“But O.J. doesn’t care. He knows he’s never going to get out of prison, so he refuses to take care of himself.”

Dr. Daniel Bessesen, a Denver-based endocrinologist who has not treated Simpson, told The ENQUIRER: “Diabetes puts you at increased risk of cardiovascular disease and stroke. About 80 to 90 percent die from heart disease, not high blood sugar.

“I’ve noticed in taking care of diabetics in correctional facilities that they become severely de­pressed, which leads to little interest in self-care.”

O.J. apparently doesn’t care about what other people think of him either. Recently, while watching TV, he confided to a close prison pal: “You know, everybody believes I killed Nicole. Well, I did do it! I need to tell someone before I die.’ ”

O.J. then revealed what happened on the night of June 12, 1994, when he went to Nicole’s town­house, seething over her drug use and the lovers she’d taken since their divorce.

He told his prison buddy he went there intending to have it out with Nicole, but got angrier and angrier along the way.

“By the time he confronted Ni­cole, he was in an out-of-control rage,” said the insider. “She kept smarting off to him, which made it worse.

“He had a knife in his pocket, and although he said he never in­tended to use it, he was suddenly hacking away with it. Then he heard footsteps rushing at him, and a strong, young guy was on him.

“He stabbed and stabbed and finally the young man (Ron Goldman) was dead. He said he still loves Nicole and remains haunted by his moment of rage.”

O.J. plans to stun the world once again when he dies, said a friend. “He’s going to write a letter con­fessing that he killed Nicole and Ron, and he’ll leave instructions that the letter be released to the public after he’s gone.

“He’s also making sure that none of his money or any other assets get to Ron’s father (who won a 1997 civil lawsuit against him for $21 million).

“O.J. has only a few pals he  can trust, so he is having them quietly hide his money in various offshore accounts with instruc­tions to give it only to his family when he dies.”

Most days Simpson just lies around his cell, said the source. “When he does get up, it’s to eat fatty and starchy junk food, especially his favorite, ice cream sandwiches.

“He’s been told by a doctor he desperately needs to get his weight down and immediately im­prove his diet or else. He was also told he could have a stroke, and he’s showing signs of it. Broken blood vessels in his eyes indicate he may already have blood clots forming.”

In May, O.J. appeared in court in his bid for a retrial. He was ridiculed in the media for being fat, and afterward he made some token efforts to exercise before giving up. Now, he keeps to him­self and, for some strange reason, repeatedly sings the Scarecrow’s song from “The Wizard of Oz” – “If I Only Had a Brain,” say sources.

“O.J. is a broken man, who is in his own little world and says he would rather die now than to be locked up like a wild animal for the rest of his life,” noted another one of O.J.’s friends.

“He ignores people when they talk to him and often wanders around in a glassy-eyed trance. His fam­ily is being supportive, but he’s not paying at­tention to them either.”