"Pretty Woman" JULIA ROBERTS’ ugly family feud ERUPTS!

Julia and her half sister Nancy Motes are feuding again – this time over Nancy’s weight!

Nancy, 35, has blown up to more than 300 pounds and her movie star sister is “disgusted” by her appearance, say sources.

“Julia’s made no secret of the fact that she’s not happy that Nancy’s gotten heavy,” said a source close to the Oscar-winning actress’ husband Danny. “She thinks it’s humiliating for her and the entire family.”

Julia, 43, went out of her way to land 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 – and she believes Nancy’s obesity reflects badly on her, con­tinued the source.

Julia is also concerned that Nancy’s weight will make it difficult for her to con­tinue to care for their mother, Betty, 76, who struggles with her own health issues.

While Julia has been paying Betty’s bills, Nancy is her part-time caretaker.

“Julia has asked Nancy point-blank, ‘Who’s going to keep an eye on mom if you get sick?’ ”

Tensions be­tween the star and her sister came to a head at Nancy’s birthday party last month at Betty’s home in Los Angeles’ wealthy Pacific Palisades area.

“Julia was rolling her eyes and making cutting comments about Nancy’s weight behind her back – whispering to partygoers, ‘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 if you had enough self-respect to lose some weight!’

“At that point, Nancy told Julia to ‘go (bleep) herself ’ – thus ruin­ing the party.”

The two women have not spoken since.