Gerald Cavendish Grosvenor, the sixth Duke of Westminster and one of Britain's wealthiest landowners, has died at the age of 64.

Grosvenor's family said he died Tuesday at the Royal Preston Hospital in northwest England after becoming ill at his nearby Abbeystead Estate.

The duke's Grosvenor Estate owns 300 acres (121 hectares) in some of London's wealthiest areas.

His ancestor, Sir Thomas Grosvenor, married heiress Mary Davies and acquired what was then marshland in 1677. Over the generations the family developed the land into two of London's most affluent neighborhoods, Mayfair and Belgravia.

The 2016 Sunday Times Rich List estimated the duke's wealth at 9.35 billion pounds ($12 billion).

Buckingham Palace said Queen Elizabeth II was sending a message of condolence to the duke's family.