The 84-year-old Singing in the Rain superstar tragically passed on Dec. 28, just a day after her Star Wars daughter died.
"While Debbie lost many millions in her lifetime to scheming husbands and bad business decisions — and even went bankrupt — she was worth a fortune when she died," says a source.
"She left the bulk of her $70 million estate to her children with Eddie Fisher, Carrie and Todd, and her granddaughter, Billie Lourd.
"She never thought for a minute that Carrie would die before her and didn't plan for it. Then Debbie herself passed away so suddenly before changing her will.
"I'm told Billie — Carrie's only child — believes her mother's share should pass straight to her."
That's because if Debbie had died first, Carrie would have received her inheritance — and when Carrie passed, it would have gone to Billie, says the source.
"Friends are bracing for a family war.
"It's so sad. Debbie would be devastated."
Billie will inherit Carrie's $5 million estate, according to insiders.
The family feud was apparent at the public memorial service for Debbie and Carrie, say sources.
Billie, 24, shockingly boycotted the event — opting to spend time with her boyfriend, actor Taylor Lautner, and her father, Bryan Lourd.
The family also has been rocked by a fight after Todd, 59, banned his half-sisters, Joely and Tricia Fisher, from participating in the memorial.
Joely posted an outrageous photograph at the service showing her "giving the finger," alongside the caption: "We were told we were not part of the 'show.'"
A rep for Todd confirmed Joely was furious — adding her post makes it clear "why Todd did not include her."
But the rep says Billie and Todd "have a great relationship" and Billie didn't attend the memorial because she was still grieving.
The source hopes that's really the case. "Debbie and Carrie would be horrified" about any bad blood, says the insider.
"Family was so important to them, and all this would break their hearts!"
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