The late Duke of Westminster, a Knight of the Garter, was a close friend of the royal family.
His wife Natalia is one of Prince William’s godmothers and their son Hugh, now 7th Duke of Westminster, is godfather to Prince George.
Buckingham Palace: “I can confirm that Her Majesty the Queen is aware of the news about the Duke of Westminster.
“A private message of condolence is being sent by the Queen and the Duke of Edinburgh.”
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 added.
Gerald Cavendish Grosvenor died at the Royal Preston Hospital in Lancashire on Tuesday after suddenly become ill on his Abbeystead Estate.
A friend of the Royal family, he became the sixth Duke of Westminster in 1979. A spokeswoman said: “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.”