Gerald Cavendish Grosvenor, Britain’s biggest landowner, has died aged 64 due to a sudden illness.
The billionaire, known to be worth £8.3bn, owned swathes of land in London.
According to Forbes, he's the third richest person in the UK and the 68th richest billionaire in the world.
He died at the Royal Preston Hospital in Lancashire today after suddenly becoming ill on his Abbeystead Estate, a spokesman said.
"His family are all aware and they ask for privacy and understanding at this very difficult time," he added.
"No further comment will be made for the time being but further information will follow in due course."
The Prince of Wales and Duchess of Cornwall are "deeply shocked and greatly saddened" by the sudden death of their friend the Duke of Westminster, a Clarence House spokeswoman said.