The Duke of Westminster Gerald Cavendish Grosvenor died aged 64 at the Royal Preston Hospital in Lancashire on Tuesday. He had become ill while on his Abbeystead Estate, according to multiple reports.

The Duke was the richest landholder in Britain with a fortune estimated to be about £9.3B, largely based on his real estate that encompasses most of the smartest addresses in London.

The estate includes 190 acres in Belgravia, including freehold properties in Eaton Square, Motcomb Street, Elizabeth Street, Pimlico Road and Ebury Street. In Mayfair, the Grosvenor Estate owns a mix of residential, retail and office buildings around Mount, Grosvenor, North Audley, Duke and Park streets. The family maintains other holdings throughout Britain and Ireland, but it is the London estate that is most strongly associated with the name.

The Duke’s third child and only son, Hugh Grosvenor, is now the 7th Duke of Westminster and heir to the vast landholdings. At age 25, he is Prince George’s youngest godfather.