Top trainer Emanuel Steward, a former amateur boxer who worked with several world champions and was also a respected television commentator, died in a Chicago hospital on Thursday aged 68.
"He has passed - he's gone home," Steward's sister Diane Steward-Jones told the Detroit Free Press by phone. "He was in no pain, and we sang to him, as well as did the doctors present. He had loved ones around him."
Steward's girlfriend Anita Ruiz, who is also executive director of the Kronk Gym Foundation, told Reuters the trainer had died after having "complications through surgery" for diverticulitis.
Steward ended his amateur career with a record of 94 wins and three losses but is best known as the trainer who transformed Thomas Hearns from a light-hitting boxer into a devastating puncher.
Under Steward's guidance, 'Hitman' Hearns became a four-division welterweight champion in the 1980s as he vied with fellow boxing greats such as Sugar Ray Leonard, Roberto Duran and Marvin Hagler.
Most recently, Steward trained heavyweight world champion Wladimir Klitschko before he was forced to step aside because of an undisclosed illness.
The West Virginia native was central to the famous Kronk Gym in Detroit where he helped shape the careers of fighters such as Hilmer Kenty and Milton McCrory. Later he worked with British and Canadian world heavyweight champion Lennox Lewis.
An inductee of the International Boxing Hall of Fame and the World Boxing Hall of Fame, Steward also worked for many years as part of HBO's commentary team on fights.
"There are no adequate words to describe the enormous degree of sadness and loss we feel at HBO Sports with the tragic passing of Manny Steward," Ken Hershman, president of HBO Sports, said in a statement.
"For more than a decade, Manny was a respected colleague who taught us so much not only about the sweet science but also about friendship and loyalty.
"His energy, enthusiasm and bright smile were a constant presence. Ten bells do not seem enough to mourn his passing." (Reporting by Simon Evans in Miami; Editing by Mark Lamport-Stokes)