The EastEnders actor died at the age of 71 this morning.
It has not been confirmed how the star died however, according to the Daily Mirror, neighbours revealed that he was battling “terminal lung cancer”.
A painter, 60, who was working on the Twickenham house where he was staying, also told the newspaper: “I said to him, ‘You alright Les?’ He said: ‘I’m fine,’ but from the outside he looked bad.
“He was positive about it all but once you get cancer… He was saying he had it. He said he had it and it went but it came back. He didn’t have much on him.”
Express.co.uk contacted a representative for the star, but they declined to comment at this time.
The sad news was confirmed in a statement from his representative today, which read: “We formally announce the loss of Leslie Grantham, who passed away at 10.20am on the morning of Friday June 15 2018.
“There will be a private funeral which will be attended by close family and friends only.”
Leslie was reported to have been in hospital earlier this week, with a representative for the actor telling Express.co.uk on Monday: “Leslie Grantham remains poorly and is being taken care of by medical staff.”
The actor is best known for his role as “Dirty” Den Watts in the BBC soap EastEnders.
Leslie first played the role of the evil character between 1985 and 1989, before returning to Albert Square back in 2003.
The character made his final appearance in the long-running show 13 years ago, in 2005.
“His ex-wife and sons have asked for their privacy to be respected at this difficult time, and for there to be no approaches to them for information or comment.
“They will not be making any statements to the media. They also ask that no photographs be taken of them in their grief.
Dirty Den appeared in the first ever episode of EastEnders, and became known by millions as the adulterous Queen Vic landlord.
Leslie previously spoke out about the BBC soap, revealing he thought it had changed.
Speaking to the Press Association, he said: “With Den and Angie (played by Anita Dobson), one minute he’d make you laugh, the next he’d cut your legs off. There was humour. Everyone thought Den was a lovable rogue. He wasn’t evil, he was just Jack the lad.
“When he came back a second time, he suddenly became this Machiavellian character. I’m not saying it was better when I was in it, but when you’re doing four episodes a week, you can’t keep up that level of consistency.”
The actor leaves behind three children, which he shared with his ex-wife, actress Jane Laurie.
The couple married back in 1981, but divorced in 2013 after more than 30 years of marriage.
Back in 1966, Leslie, then a teenager, was convicted of murdering a German taxi driver while serving as a soldier – a charge he always denied.
The star served an 11-year sentence at Leyhill Open Prison in Gloucestershire, which he later returned to as a VIP guest to open an art exhibition.
Leslie previously said the jail fostered his interest in amateur dramatics.
Back in 2004, the actor was exposed after taking part in webcam sex sessions from his EastEnders dressing room at Elstree Studios.
Leslie issued an apology following the scandal, which had also seen him criticise his co-stars, and described his actions as “a moment’s stupidity” of which he was “wholeheartedly ashamed”.