Ja Rule slams 50 Cent in his new book, alleging cooperation with the authorities.

Just when it seemed the beef between rapper Ja Rule and 50 Cent had been put to rest, Ja Rule is waking it back up in a big way.

In his new book, “Unruly,” the Queens rapper, aka Jeffrey Atkins, rehashes his 14-year-old feud with fellow music man Curtis “50 Cent” Jackson, in which he accused the “In Da Club” singer of snitching.

“When they (the feds) asked him who he thought had shot him, it would make sense that 50 would have said, ‘Ja Rule, Irv Gotti and Murder Inc.,’ ” writes Ja Rule, referring to a 2000 attack that left Fitty hospitalized with nine gunshot wounds.

50 Cent later said he never cooperated with law enforcement, even when they came to him trying to make a case against Ja Rule’s rap-mogul colleagues Irv “Gotti” Lorenzo and Irv's brother Chris, who were eventually acquitted of laundering drug money through their label, Murder Inc., in 2005.

But Ja Rule, 38, claims that case couldn’t have been made without 50 Cent. “He secretly led them through his recordings for the answers they were looking for,” Ja Rule insists.

In 2011, Ja Rule and 50 Cent publicly made amends. But in his new book, Ja Rule recalls a 2000 peace summit in Atlanta between the two that didn’t go so well.

“50 tried to swing on me, but I dipped, then I hit him with the baby Louisville Slugger,” says Ja Rule, who came armed with a baseball bat. “Bam! I dropped the bat. I pulled the shirt over his head. I started catching him left, right, uppercut.”

According to Ja Rule, Fitty’s crew turned tail and ran. Ja Rule also claims he led the charge in the notorious Hit Factory recording studio attack in Midtown later the same year when 50 Cent was stabbed. Ja Rule says he armed himself with a crutch swiped from a crew member who had a broken foot and slammed into the recording studio with his crew.

“I hit him with the crutch,” brags Ja Rule. “We proceeded to whip his ass. I was putting in my work. 50 was crunched in the corner. I slammed the big Tannoy speaker down on him.”

Ja Rule defends himself, saying that because of his success, “50 was a crazed man on a mission to destroy me.”

Ja Rule is now shopping a reality show “Follow the Rules,” set at home with his wife, Aisha, and their three children. His book “Unruly: The Highs and Lows of Being a Man” is out next Tuesday.