The episode left Italy stunned, not simply because of the cocktail of drugs consumed by this scion of the country’s tragedy-stricken “royal family”, but by the sordid circumstances in which he was found — a blow to the Agnelli image.

Handsome, energetic and extrovert, Signor Elkann, 28, is the grandson of Gianni Agnelli, the late patriarch of Fiat, who doted on him and whom, in many ways, he resembles. As the marketing manager of Fiat and a director of Juventus Football Club, he was the public face of the efforts to reinvigorate the ailing industrial giant.

Last night doctors in Turin said that Signor Elkann was recovering from the effects of a “lethal cocktail” including cocaine, heroin and alcohol. He was under sedation, but out of danger.

Il Giornale reported: “Lapo was taken ill not at a fashionable party but in questionable company in the back streets of Turin.” It said that “a symbol has fallen in the dust”, a play on the Italian word polvere, which also means powder, a reference to cocaine. Possession of cocaine for personal use is not illegal in Italy, but dealing in it is.

Police said that the three men being questioned had denied bringing drugs to the flat where Signor Elkann collapsed. Officers added that Signor Elkann was unconscious and in a critical condition when admitted to hospital.

In an interview with La Repubblica, Patrizia, who said his real name was Lino, claimed that Signor Elkann had rung his doorbell at 3am.

“We’ve known each other for a few months,” he said. He said that they had all fallen asleep at dawn. “I woke about nine and tried to wake Lapo, but he gave no sign of life. I immediately called an ambulance.”

Signor Elkann is the son of Alain Elkann, the writer, and Gianni Agnelli’s daughter Margherita. The Agnelli family’s hopes rest on Signor Elkann’s older and more conventional brother, John Jacob, 29, who is the deputy chairman of Fiat.

Lapo Elkann has featured frequently in gossip columns for his playboy lifestyle. Gianni Agnelli, who died in January 2003 at 81, also lived life in the fast lane as a young man.

Lapo Elkann has worked hard, however, to relaunch the century-old Fiat brand at a time when the company’s core car business is in difficulty, flamboyantly marketing the Fiat logo on sportswear, shoes and bags aimed at the young. He learnt the trade as a Fiat shopfloor factory worker at the age of 17, later maintaining his family’s international connections as Henry Kissinger’s personal assistant.

But tragedy has always shadowed the Agnelli dynasty, drawing comparisons with the Kennedys. Agnelli’s father, Edoardo, was killed at 42 in a seaplane accident in 1935, when Gianni was 14. His mother, Virginia, an Italian princess, died ten years later when her car collided with a lorry.

To Agnelli’s disappointment, his son, also Edoardo, showed no interest in industry and was instead drawn to Eastern religions and drugs. He committed suicide five years ago by jumping off a motorway viaduct.

The other obvious heir, Agnelli’s nephew Giovanni Alberto, died of a rare cancer in 1997, forcing the dynasty to jump a generation and groom John and Lapo for the top.

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