The Duchess of Cornwall's father Major Bruce Shand has died at the age of 89, Clarence House said.
Camilla was 'devastated' by Maj Bruce Shand's death
The former Cavalry officer died at his home in Dorset on Sunday morning with his family around him.
Maj Shand had a distinguished military career, winning two Military Crosses in World War II before becoming a wine merchant and huntsman.
The Duchess of Cornwall was said to be "absolutely devastated", a Clarence House spokesman said.
"He had been unwell for sometime and his family was with him when he died at his home in Dorset.
"Arrangements are being made for a private family funeral and we ask the media to respect the family's privacy," he added.
Maj Shand lived with his daughter Annabel near Blandford Forum in Dorset.
Camilla has cancelled her engagements for a week, and is unlikely to attend further birthday celebrations for her mother-in-law, the Queen, on Thursday.
Charles was also upset at Maj Shand's death.
"He was extremely fond of the Major and is very upset at the news," a spokesman said.
Prince Charles once described him as "the gallant major".
The major's coat of arms was included in the duchess's own design when she married Prince Charles in 2005.
Major Shand was Vice Lord Lieutenant of East Sussex and Master of the South Down Hounds for 19 years.
His wife, Rosalind, died in 1994, aged 72 from osteoporosis.