His character, "Dirty" Den Watts was central to several iconic EastEnders storylines, including getting his daughter's best friend pregnant at 16, being assassinated by a crook hiding behind a bunch of daffodils in 1989.
Leslie's passing comes days after he was reported to be in a critical condition in the United Kingdom having returned from Bulgaria, where he had been living.
The Loose Women Twitter account also shared: "Sad news today - EastEnders actor Leslie Grantham, who played Dirty Den, has died aged 71".
One storyline helped the BBC soap pull in its biggest-ever audience, when more than 30 million viewers tuned in to see him hand over divorce papers to wife Angie on Christmas Day in 1986.
He wrote: "What a life Leslie Grantham led". He had been living in Bulgaria but returned to the United Kingdom for hospital treatment.
"We formally announce the loss of Leslie Grantham, who passed away at 10:20 am on the morning of Friday 15th June 2018".
'His ex-wife and sons have asked for their privacy to be respected at this hard time'.
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EastEnders's executive consultant John Yorke paid tribute on behalf of the BBC soap, saying: "Everyone at EastEnders is deeply saddened to hear that Leslie has passed away".
"We extend our deepest sympathies and condolences to his family and friends at this extremely hard time".
According to The Sun, close friends and pals in the showbiz industry had been visiting him in hospital this week.
Prior to his EastEnders career, in 1967 he was convicted of murdering a German taxi driver while serving as a soldier, which he has always denied, and he went to prison until 1977.
He is thought to have been in Bulgaria to star in a TV series called "The English Neighbour".
"He was a wonderful and special actor, witty and very talented".