NATALIE WOOD’S daugh­ter COURTNEY was recently arrested for coke and her­oin possession – and sources say she spiraled out of control when the investigation into her famous mother’s drowning death was reopened last year.

In an exclusive interview with The ENQUIRER, the tragic actress’ sister Lana Wood revealed that Courtney, whose dad is actor Robert Wagner, refused to cooperate with police looking into the cold case. And she turned to drugs in despair.

“My sister would be devastated if she knew how Courtney has ru­ined her life,” Lana said.

 “She was Natalie’s golden girl – the child she always longed for with R.J. (Wagner).

“She was rushed to the hospital some years ago after attempting suicide, but in the past few years the poor girl has become an emotional tragedy. For a time she was receiving psychiatric care.

“I’m sure that if Natalie had been around to look after her and watch her grow up, Courtney wouldn’t have wound up in a jail cell. This is a terrible tragedy.”

Lana said that already-troubled Court­ney, 38, went “over the edge” after police showed up at her Malibu home last year to discuss her mother’s death.

Natalie drowned under sus­picious circumstances on Nov. 29, 1981, during a tu­multuous night on the yacht “Splendour” with her husband, Wagner, and actor Christopher Walken. Following new claims by “Splendour” captain Den­nis Davern, who’d written a book about the tragedy, police reopened the tragedy last No­vember. But they closed it again after just a few months of in­vestigation.

“When Courtney heard the case was being reopened, and that her father could be ques­tioned as a ‘person of interest,’ it was more than she could bear,” said a friend. “Courtney was just 7 when her mom died, and she was raised by her father and a nanny. Maybe this arrest will be a wake­up call.”

Courtney was busted on April 22 for cocaine and heroin possession after police responded to a shot­gun blast at her home. Her boyfriend, Matthew Cox, 34, was also arrested.

On April 30, after news of the incident broke, a spokesman for Malibu/Lost Hills Sheriff ’s Station told The ENQUIRER: “As deputies investigated the incident, they recovered several handguns and several baggies of what appeared to be narcotics at the location.

“Mr. Cox was placed under arrest for suspicion of discharging a firearm in a negligent manner and Ms. Wagner was placed under arrest for sus­pected possession of narcotics.”

They were booked at the jail and released. Courtney was required to post $10,000 bail.

Her aunt Lana told The ENQUIRER: “She was a stunning child and just so young when Natalie died. Both parents doted on her.

“But R.J.’s love hasn’t saved her from a life that’s spiraled out of control.”