Tensions between the feuding members of the country's first family of showbiz have blown up into full-scale war, with Hallyday's biological children challenging his "rewritten" will, in which he left everything to his fourth wife Laeticia, 32 years his junior.
The fractured family was able to maintain a unified front for the funeral of the "French Elvis" in December, when hundreds of thousands of his fans thronged the centre of Paris for a "national popular tribute". But that uneasy truce exploded when details of the rocker's will became known on Monday.
Not only was his daughter, actress Laura Smet, "stupefied and hurt" that she and her half-brother David Hallyday had been left nothing, with everything going to Laeticia and eventually the two Vietnamese girls she and Hallyday adopted. But she also seemed to confirm long-running rumours that Laeticia was jealous of Smet's relationship with her father, who died at the age of 74 after a battle with lung cancer, and prevented him from seeing her.
Smet said that the woman the press had once dubbed Hallyday's "Iron Lady" had kept her from Hallyday's deathbed.
"All those times when we had to hide to see and call each other," Smet wrote in an emotional open letter to her father, which she released through AFP.
"It is still killing me not to have been able to say goodbye to you, Papa -- do you know that at least?" she added.
In-laws and outlaws
The revelations raised questions about the hold Laeticia and her father -- disgraced nightclub owner Andre Boudou -- seemed to have over Hallyday, whose fortune has been estimated at between €50 and €100 million ($62 million and $124 million).
Laeticia met the star when she was 20 and he was 52 in her father's Miami nightclub.
Boudou -- who French judges sentenced to six months in jail for tax and social security fraud in 2007 -- was instrumental in persuading Hallyday to leave Universal Music in 2004, a move that cost the singer much of his back catalogue.
A Paris nightclub they had opened together folded the same year.
Boudou's mother Elyette, 82 -- nicknamed "Granny Rock" -- heads the three companies which control Hallyday's royalties, and she also co-owns the Paris mansion in which the star died, which he had signed over to his wife four years ago.
Hard-living Hallyday was notorious for his cavalier attitude to both money and taxes. He was often spectacularly open-handed with his friends, offering one an Andy Warhol painting he had admired, and flying others across the world to parties in his homes in Los Angeles, the Swiss ski resort of Gstaad and his Caribbean bolthole of Saint Barts.
Power behind the throne
Laeticia, 42, was credited with bringing order to his household. So much so that in 2009, after he almost died on the operating table after a routine operation, Hallyday was forced to publicly deny that she was the real power behind the throne.
As the years rolled by the couple spent more and more time in California, where their adopted children went to school.
Unlike France, inheritance laws there also allow children to be disinherited. A fact that became shockingly apparent this week to the many Hallyday fans who railed against Laeticia on social media.
The singer's best friend, fellow French rock legend Eddy Mitchell, joined them Friday by telling AFP, "I don't understand how anyone could disinherit their children. As Laura's godfather, of course I support her."
His intervention came after the leak of documents showing Hallyday made monthly payments to Laura and her half brother, mostly to pay mortgages. Then Elyette Boubou told French television that she "didn't think much of Laura and David, they have already had their part (of Hallyday's wealth)."
But his first wife, 1960s pop star Sylvie Vartan, shot back within hours, telling AFP that she was "dismayed by the false information which is being purposely circulated" to undermine her son. She said it was her part of the marital home which she asked Hallyday to give to David as part of their divorce settlement in 1980.
Vartan said she was "horrified" that her son "had been deprived of the artistic heritage of his father, which I cannot tolerate, and that is why I have broken my silence."
By AFP's Fiachra Gibbons