A sinister cover-up occurred after ROBERT WAGNER’s wife NATALIE WOOD disappeared and subsequently drowned 30 years ago – and now sources claim the TV legend is terrified that dreadful night will come back to haunt him!

That’s the shocking theory behind law enforcement authori­ties’ decision to reopen the case surrounding the beloved actress’ death, The ENQUIRER has learned.

While authorities say the “Hart to Hart” star is not a suspect in the tragedy, the new probe has him “sweating out just what will be revealed about the night Natalie died,” a close fam­ily friend told The ENQUIRER.

“This is Robert’s worst nightmare,” the friend said. “Investigators plan to reexamine every last detail of that drug-fueled, boozy night and exactly what happened as his wife plunged into the sea.”

It has long been believed that the “West Side Story” actress, then 43, slipped off the yacht Splen­dour around midnight on Nov. 29, 1981, and drowned off the coast of California’s Catalina Island. But details from the fateful night – from Splendour’s captain Dennis Davern have convinced investiga­tors to further look into the case.

According to Davern, Natalie had been drinking and taking Quaaludes with her husband and close friend Christo­pher Walken when Wagner became enraged, believing that Walken was flirting with his wife. According to author Marti Rulli, who co-authored the book “Good­bye Natalie, Goodbye Splendour” with Davern, Wagner smashed a wine bottle on a table and yelled at Walken: “What do you want to do, (bleep) my wife? Is that what you want?”

Walken went to sleep in his cabin, while Wagner and Wood returned to their stateroom, where a loud argument broke out.

“Dennis made an attempt to stop it, and was told to go away by Wagner,” Rulli said in an in­terview. “Later, Natalie was missing.”

Davern told a reporter Wagner refused to let him notify the Coast Guard that Natalie had disappeared or employ any search methods.

When asked if he believed Wagner was re­sponsible for Wood’s death, Davern answered: “Yes, I would say so. Yes. We didn’t take any steps to see if we could locate her.”

While Wagner’s publicist issued a statement saying that the fam­ily supported an investigation based on “valid” evidence, the friend be­lieves Wagner is deeply concerned that reopening the case will cast him in an even more unfavorable light.

“R.J.’s well aware that there are people out there who believe that he didn’t do enough to rescue her,” said the friend.

“And now that every minute of that fateful weekend is going to be reex­amined, he must be terrified.”