Speaking at a press conference this afternoon at the Boscolo Exedra Roma Hotel, Michael Kobold said Gandolfini "experienced a medical emergency" at around 10.00pm yesterday.
The owner of luxury brand Kobold Watch Company, of which Gandolfini was an ambassador, said the actor was like a "big brother" to him.
Speaking on behalf of the family, Kobold said "the hotel notified emergency crews who administered first aid before taking James Gandolfini to hospital". "He died of an apparent heart attack," he added.
Kobold was unable to say which family member found Gandolfini, although international media have stated his teenage son was travelling with him in Italy.
The 51-year-old star was due to appear at the closing ceremony of Sicily’s Taormina Film Fest this Saturday.
Reacting to the news, US broadcaster HBO said: “We’re all in shock and feeling immeasurable sadness at the loss of a beloved member of our family...He touched so many of us over the years with his humor, his warmth and his humility.”
HBO screened six series of the Sopranos and in 2006 Gandolfini won three Emmy awards.
As news of Gandolfini’s death broke, tributes poured out from the acting community. Writing on Twitter, across Susan Sarandon described the actor as “one of the sweetest, funniest, most generous actors I’ve ever worked with”, while filmmaker Michael Moore said he was “one of the good guys”.
The governor of Gandolfini’s native New Jersey, Chris Christie, said the news came as an “awful shock” and praised the actor as “a true Jersey guy”.
Born in 1961 to parents of Italian descent, Gandolfini went on to study communications at Rutgers University. Before turning to acting he worked as a truck driver and in a bar.
A friend persuaded Gandolfini to taking an acting class and after a string of smaller parts he was cast as mafia boss Tony Soprano in 1999, the role which shot him to fame.