The Duchess of Cornwall was in mourning last night following the death of her father Major Bruce Shand.
The 89-year-old former Cavalry officer died at his home in Dorset yesterday morning with his family at his bedside.
Camilla was said to be "absolutely devastated", a Clarence House spokesman said.
Major Shand had been unwell for some time.
The spokesman said he died of natural causes just after 10am, and had previously fought cancer.
The Duchess was close to her war hero father, who was awarded a Military Cross and bar. A spokesman for Camilla said: "She's absolutely devastated and she's with her family."
The Duchess's engagements have been cancelled for this week and at this stage she is unlikely to attend commemorations on Thursday to mark the Queen's birthday.
The Prince of Wales was also said to be greatly upset at his father-in-law's death.
"He was extremely fond of the Major and is very upset at the news," said the spokesman.
The Major was a source of support for Camilla, especially during the intense publicity she faced throughout the 1990s when her relationship with Charles came to light.
He lived with his daughter Annabel near Blandford Forum in Dorset.
Major Shand is credited with having helped keep Camilla strong during the years when she faced condemnation as a marriage wrecker.
In 2005, the proud Major finally saw his daughter marry the Prince of Wales and become an HRH and the Duchess of Cornwall.
The former wine merchant came to be admired by the Prince who gave him an apartment at Clarence House.
A first-class horseman, Bruce Shand emerged from Rugby to join the Army as a second lieutenant in the 12th Royal Lancers.
When war broke out in 1939, he became a hero to his fellow officers and men by earning two Military Crosses - Military Cross and Bar - in the shortest possible space of time.
In the lead-up to the battle for El Alamein, he met wartime Prime Minister Winston Churchill, on a surprise morale-boosting trip, who had singled him out because of the ribbons on his chest.
Churchill remarked: "You're a very young man [to have won two Military Crosses]. How splendid. But you look so thin." Shand, then 25, was destined to become thinner.
He was shot and captured immediately after El Alamein - the battle that changed the course of the war in North Africa.
On the night of November 6, 1942, he was leading his squadron forward when they encountered the enemy.
As he later recalled in his memoirs, Previous Engagements: "Something like a whiplash stung my cheek and Sergeant Francis beside me slumped to the bottom of the car with a large hole in his chest, killed instantly."
His vehicle was hit again, killing the driver Corporal Edward Plant and bursting into flames. Shand was hit a second time and was captured and taken prisoner.
"I do not remember hitting the ground. A buzz of German voices greeted my return to consciousness," he wrote.
The bullet that killed Sgt Francis had gone through theMajor's cheek. The near fatal war wound left a permanent scar under the Major's eye.
In March this year Camilla travelled to El Alamein with Charles on her tour of Egypt to pay an emotional tribute at the graves of her father's two fallen comrades.
Camilla placed bunches of cream roses at the foot of their tombstones, and left a hand-written note from her father, who, by this stage, had been ill for some time
Major Shand wrote: "The gallantry and sacrifice of two fellow 12th Lancers on 6th November 1942 will never be forgotten by me."
Camilla, clearly moved, said after the visit: "I'm so pleased that I've done it for my father."
Spending the rest of the war as a prisoner-of-war in Germany he returned to Britain and went on to marry the Honourable Rosalind Cubitt, daughter of Lord Ashcombe.
The couple's first child, Camilla, was born in 1947.
In later life he was to live in East Sussex, becoming the county's Vice Lord Lieutenant, representing the Queen on official occasions, and later a member of the Queen's Body Guard of the Yeomen of the Guard.
He was to play host to the Prince of Wales before his daughter's engagement to Andrew Parker Bowles.
In 1992, Camilla accompanied him to an El Alamein memorial service at Westminster Abbey in the presence of Diana, Princess of Wales, amid intense press scrutiny.
Through the years that followed, the Major led a quiet and unshowy life. In a warm tribute at his marriage last year, the Prince described his new father in law as the "Gallant Major", adding: "I am proud to be your new son-in-law." ..SUPL: