JULIA ROBERTS’ half-sister Nancy Motes committed suicide – and the Oscar winner is said to be wracked with anguish about it.

The death was originally reported as a suicide – a final COD determination will take weeks – and the source said Julia “wishes she could have talked to her and worked out their differences, and she’s heartbroken that it’s now too late.”

Sadly, Nancy, 37, a former production assistant on the TV show “Glee,” took her own life in Los Angeles, Calif., on Feb. 9.

“Nancy felt she was at the end of her rope,” said the source.

Meanwhile, Nancy’s fiancé John Dilbeck was the one who found her lifeless body and he lashed out in grief at the family.

According to an official at the Los Angeles County Coroner’s office, Nancy – who’d been suffering from depression – was pronounced dead at 2:12 p.m. of an apparent overdose.

She was found in the bathtub at 1000 N. Bundy Drive in Los Angeles.

“Nancy was a dog-walker and she had gone over to a client’s house to walk his dog while he was out of town,” revealed a family insider.

“She’d taken her prescription medications with her – antidepression drugs and anti-anxiety tablets – and swallowed a bunch while she was in the bathtub.”

Meanwhile, her fiancé John became alarmed when he repeatedly called Nancy on her cell phone and she didn’t pick up.

He went to her client’s house – and to his horror, found her dead.

Devastated, he called up Julia’s sis­ter Lisa Gillan and, according to the source, unleashed his rage.

The source revealed: “Lisa was thunderstruck and, when Julia found out, she became hysterical.

“She’s been crying her eyes out ever since.”

In a statement, Julia and her fam­ily – including Lisa Roberts Gillan and brother Eric Roberts – said: “It is with deep sadness that the family of Nancy Motes…confirms that she was found dead in Los Angeles yesterday of an apparent drug overdose…The family is both shocked and devastated.”

The women’s mother, Betty Motes – who lives in a home Julia bought her near Pacific Palisades, Calif. – was in the hospital at the time of Nancy’s death, undergoing tests.

“She was due to be released but was so over­come with emotion that she decided to stay at the hospital because her blood pressure had soared,” said the family insider.

“This was not an accidental overdose on Nancy’s part – far from it. She had planned this.

“The police informed the family that they had found envelopes addressed to Lisa, Julia, (their mom) Betty and (Nancy’s fiancé) John.”

The contents of the notes have not been released.

As ENQUIRER readers know, Julia and her half-sister Nancy had been feuding for years.

The sisters had a difficult relationship, and a source says Nancy blamed Julia for constantly belittling her.

In 2005, we revealed how Julia exploded when she caught Nancy snapping pictures of her then-newborn twins Hazel and Phinnaeus at the actress’ home in Taos, N.M.

The two also got into a heated fight when Julia made disparaging remarks because Nancy had blown up to 300 pounds.

“Julia thought Nancy’s weight was humiliating for her and the entire family,” divulged a source close to the star’s husband Danny Moder.

Despite their differences, Julia landed Nancy a job as a produc­tion assistant on the TV show “Glee,” thanks to her connections with the show’s creator, “Eat Pray Love” director Ryan Murphy.

“Everyone thought that hos­tility between the two would relax after that,” said the source. “But instead, things just got worse.”

Tensions between Julia, 46, and her sister exploded into the open at Nancy’s birthday party in May 2011 at Betty’s home.

“Julia was rolling her eyes and making cutting comments about Nancy’s weight behind her back,” said the source. “She whispered to party- goers, ‘Can you believe how big she’s gotten?’

“When Nancy got wind of what Julia was saying, she confronted her, telling her to shut up and leave her alone.

“Julia shot back, ‘Well, I wouldn’t have to (bring it up) if you had enough self-respect to lose some weight!’

“Nancy told Julia to ‘go (bleep) yourself’ – ruining the party.”

But the criticism through the years did convince her to do something about her weight. Nancy underwent gastric bypass surgery and eventually slimmed down to 155.

Last year Nancy suffered a severe financial blow when she was dumped from “Glee.”

Depressed, Nancy had little or no money and hefty bills, including a $30,000 debt for her gastric-bypass operation. Said the source: Nancy may have “felt that suicide was the ONLY way out.”