Nottingham Forest owner Nigel Doughty has been found dead at his home. He was 54.
The club said Doughty was found in the gym at his Lincolnshire house.
"It is with enormous sadness that Nottingham Forest announce the death of the club's owner Nigel Doughty," the club said in a statement.
"Mr Doughty, who was 54, was found dead earlier today in his gym at his home in Skillington, Lincolnshire.
"The club would like to appeal for the privacy of Mr Doughty's family to be observed at this sad time.
"The club will be making no further comment."
Life-long Forest fan Doughty stepped down as chairman in October after a decade in the job following the sacking of former England manager Steve McClaren.
He was replaced in the role by former Forest player and manager Frank Clark.
Doughty, who saved the Reds from administration when he bought the club for £11million (Dh63.8m) in 1999, has invested almost £100million of his personal fortune in the club.
Forest players and Nottinghamshire sportsmen have paid tribute to Doughty on social networking site Twitter.
Forest forward Matt Derbyshire said: "I can't believe the sad news, my thoughts go out to his family," while golfer Lee Westwood, born in nearby Worksop, tweeted: "Terrible news to hear that the Forest chairman Nigel Doughty has died."
The political world also remembered Doughty, with Labour leader Ed Miliband saying: "I am shocked and saddened to hear of Nigel Doughty's death. I was with him only a week ago and he was full of life, enthusiasm and vigour.
"He was a kind, generous man with a deep desire to make the world a better place. My heart goes out to his wife Lucy and his children. We mourn his death deeply and will sorely miss him."
Doughty had led a Small Business Taskforce which made recommendations to Labour late last year which are to be considered as part of the party's policy-making process.
As a Forest fan, Doughty's dream was to guide the club back into the Premier League.
During his 10 years at the City Ground, the club won promotion back to the Championship in 2008, three years after their relegation.
Under manager Billy Davies, the Reds reached the play-offs in each of the last two seasons.
Forward Garath McCleary praised Doughty for the work he did, saying: "He has done so much for Forest, which was not always best appreciated. My thoughts are with his family."
Nottinghamshire and England cricketer Stuart Broad added: "He was a lovely man and did a huge amount for Forest."
Former Forest striker and television and radio pundit Stan Collymore said: "Nottingham Forest owner Nigel Doughty has sadly passed away today. Condolences to his family and friends I'm sure from everyone at #nffc."