Millwall owner John Berylson has sadly died at the age of 70 following a 'tragic accident', the club have confirmed.
The Championship side announced the news in an emotional statement on social media on Tuesday.
But they did not release any further details about his death.
The American businessman became involved with The Den outfit in 2006, then became a significant shareholder in 2007 after he led a consortium that invested in the team, who were in League One at the time.
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He replaced Stewart Till as chairman and oversaw two promotions to the Championship.
Berylson is survived by his wife Amy and his three children Jennifer, James and Elizabeth.
Millwall's statement reads: "It is with a collective broken heart and the deepest of regret that we announce the passing of our beloved owner and chairman, John Berylson.
"John's sudden and tragic passing will unquestionably impact all those who were fortunate to have known him. He was a truly great man, incredibly devoted to his family, and a person of such remarkable generosity, warmth, and kindness.
"He lived a storied life, one full of colour and joy, and was infinitely thoughtful of others with an endless desire to share his immense knowledge and experiences to help people."
The club statement added: "Under John's passionate leadership and guidance, Millwall has enjoyed tremendous success and stability.
"Since first becoming involved in the club in 2006, he has presided over some of the greatest moments in Millwall's history, and his influence in providing the platform for those was immeasurable.
"John continued to speak eagerly about the new season and his vision for the future, and any success moving forward will be in his memory and honour. It will be his legacy.
"John revelled in the club's underdog status and mentality. He related strongly to such values and identity and adored Millwall supporters.
"He was fiercely loyal to all his staff, and both they and the fan base will miss him beyond measure."
Millwall fans can pay their respects in a book of condolence at the club's stadium on Wednesday, which will be shared with his family.
Nasir Jabbar