Billionaire landowner the Duke of Westminster, Gerald Cavendish Grosvenor has died aged 64.
The duke died at the Royal Preston Hospital in Lancashire on Tuesday after suddenly becoming ill while at his Abbeystead Estate, a spokesman said.
"It is with the greatest sadness that we can confirm that the Duke of Westminster, Gerald Cavendish Grosvenor died this afternoon at Royal Preston Hospital," the spokeswoman said
"He was taken there from the Abbeystead Estate in Lancashire where he had suddenly been taken ill.
"His family are all aware and they ask for privacy and understanding at this very difficult time.
"No further comment will be made for the time being but further information will follow in due course."
The father of four, who has an estimated personal fortune of £8.3bn, is believed to have suffered from a heart attack, the Daily Mail reported.
The Duke is the richest property developer in the UK through his company the Grosvenor Estates, which owns land in Oxford, Cheshire and Scotland as well as vast swathes of property in central London.
In 1970, he joined the Territorial Army as a trooper before eventually becoming the Assistant Chief of Defence Staff in 2003. He succeeded his father to become the sixth Duke of Westminster in 1979. His son Hugh is now the seventh Duke of Westminster at the age of 25.
The Duke was close with the royal family - his wife is godmother to Prince William - and he was made a Commander of the Royal Victorian Order in 2012 as a personal gift from the Queen.
He was never expected to accede to the peerage as his grandfather was the sixth son of the 1st Duke of Westminster, Hugh Grosvenor. But his father, Robert Grosvenor, unexpectedly became Duke in 1967 after the death of his brother and cousin, making him heir to a hugh fortune.
A Buckingham Palace spokeswoman said: "I can confirm that Her Majesty the Queen is aware of the news about the Duke of Westminster. A message of condolence is being sent by the Queen and the Duke of Edinburgh."
Additional reporting by PA
