TWENTY years after Ni­cole Brown Simpson and her friend Ron Goldman were brutally slain, The ENQUIRER has discov­ered lost diaries that rip the lid off the REAL rea­son O.J. wanted Nicole dead.

Nicole sealed her fate only days before the sensational June 12, 1994 double murder when she wrote in her diary about her burning love for a se­cret lover – a celebrity who socialized regularly with both O.J. and Nicole.

And now an insider close to O.J. has revealed to The ENQUIRER for the first time the chilling contents of the diaries – Nicole’s final, haunting testa­ment from beyond the grave.

O.J. found the diaries at NICOLE’S Brentwood condo and flew into a mur­derous rage when a source says he read her bombshell confession: “I love XXXXX. I want to marry him. He’s the only man who has ever truly satisfied me, as a lover and a person.

“I can’t help myself. O.J. is going to kill me when he finds out how I truly feel. I fear he already knows. I’m a free woman now…I will live my life the way I want.”

O.J. had been able to get his hands on Nicole’s most private papers because he’d stolen a spare key from her condo while visiting their children, who lived with her.

“He said he wanted the keys so he could check out her place whenever she wasn’t home to see ‘what the b**** was up to,’” revealed the insider.

A little more than a week before the murders, Simpson discovered the diaries after secretly entering Nicole’s home and rummaging through her bedroom. And he blew up when he read about her gushing over his love rival. “O.J. said he ripped out the pages about Nicole and this guy,” the insider told The ENQUIRER. “Sitting in his prison cell all these years later, he still talks about it. The words are burned into his brain.

“Nicole compared her lover sexu­ally to her jealous ex-husband, and O.J. came up short. She wrote that the mystery man ‘is someone that knows how to please a woman. He’s strong but gentle and he cares. Not like O.J., who’s a selfish lover.’”

As she penned the heart-wrenching thoughts, Nicole repeatedly made it clear she felt doomed, said the insider. “She wrote, ‘O.J. can’t stand I’m with XXXXX. He will kill me for it. That’s cer­tain. He’s never going to let me go. There’s nothing I can do about it. I’m standing on my own feet now, and I’m going to live my life for me, not O.J.’”

Revealed the insider, “O.J. said those were the words that sent him over the edge,” even though Nicole and her lover didn’t begin their affair until Feb­ruary 1993, a year after she filed for divorce.

But in the wrongful death civil lawsuit leveled against O.J. by Ron Goldman’s family, Simpson insisted that he never became frustrated enough to hurt Ni­cole – even after he claimed she was having an affair with his pal and fellow football great Marcus Allen.

Under sworn testimony, Mar­cus has repeatedly denied that he had sex with Nicole. But during O.J.’s civil trial, Simpson’s lawyers brought it up. In a bid to show the fallen superstar was not possessive and did not have an explosive temper, they claimed O.J. knew about the alleged affair and still hosted Marcus’ wedding to Nike model Kathryn Eick­staedt in June 1993 at his Rockingham home. But in a deposition, Allen called Simpson a liar for saying he had an affair with Nicole.

Daniel Petrocelli, an attorney for the Goldman family, said two of Nicole’s friends gave sworn testimony in the civil trial that she had told them “she was see­ing Mr. Allen again near the very end.”

Nicole’s close pal, Faye Resnick, also said in her book, “Nicole Brown Simpson: The Private Diary of a Life Interrupted,” that Nicole admitted she was having an affair with Marcus in the last weeks of her life. Resnick wrote that she spotted Mar­cus’ car outside Nicole’s condo and asked her about it

“Faye, I dig him,” Nicole said, according to Resnick. “He makes me feel really good. And I’m entitled to happiness.”

Resnick also recalled the time Nicole picked up a large piece of driftwood while walking on the beach and compared it to Allen’s manhood. After that, she and her close circle of pals jokingly called him “Driftwood.”

Resnick claims that when O.J. found out about Marcus and Ni­cole, he was humiliated and very angry, angry enough to commit murder.

According to the insider, after O.J. and Nicole’s divorce was finalized in October 1992, Simpson became increasingly obsessed about her dating other men – and repeatedly spied on her. “Then, when he discovered the diaries, he blew up,” said the source.

“After that, O.J. began peeking through the windows of her condo trying to see if she was with someone. He even hid in the bushes, and one day he thought he saw the man in the diary entry having sex with Nicole in her living room.

“O.J. told me, ‘I later tried to talk to Nicole but she wasn’t having anything to do with me. I decided I was going over to her house to confront her about him.’ When he got to the condo, O.J. said Nicole came to the door with a kitchen knife in her hand, which infuriated him even more. He told her, ‘I know you’re screwing XXXXX. I won’t have this happening around my kids. I can’t take this crap any­more.’

“O.J. said Nicole told him to go screw himself. He said he went nuts and slashed her with a knife he often carried around. Then Ron Goldman showed up and just happened to be in the wrong place at the wrong time. Too bad for him. O.J. killed him, too.

“‘I went insane with jealousy,’” the in­sider says O.J. told him. “He believed the guy in her diaries had stolen his woman and he was going to make her pay!”

Ironically, Nicole usually stored her di­ary chapters in a safe deposit box – and The ENQUIRER previously revealed por­tions of it. But, tragically, Nicole never got to seal away her final pages – and paid for it with her life.