A former British Army commander in Afghanistan has said Prince Harry 's claims of killing 25 Taliban fighters is a security threat and could affect the safety of soldiers in the field.
Colonel Richard Kemp also believes that Harry's comments have "undermined" the positive work that he did while in the Army.
The UK's former National Security Advisor also revealed he would have advised Prince Harry against his remarks.
Kim Darroch told Sky News: “Personally if I’d been advising the Prince, I would have advised against the kind of detail he goes into.”
The Duke of Sussex said that he killed 25 Talibans during his second tour on the Helmand frontline while serving as an Apache helicopter co-pilot and gunner.
In his new book he says he blasted enemy insurgents during six combat missions which involved the “taking of human lives."
They were among 100 operational missions in which he was mostly carrying out surveillance operations and escorted other aircraft and ground forces.
Now Col Kemp, former commander of British forces in Afghanistan, has told the Mirror: "All the good work Prince Harry did on behalf of the Armed forces has been undermined by his comments.
"Not only has he gone too far in talking about this in terms of himself but it may have repercussions for others.
"As a member of Royal Family he has to accept being something of an ambassador for the UK - so his comments may effect the security of his former comrades on foreign operations …"
Most soldiers are unaware of exactly how many opposition forces they kill but Harry wrote that he knew his exact body count because of top-of-the-range military technology.
He explained that he fought “in the era of Apaches and laptops.”
But he added that: “...it seemed essential not to be afraid of that number. So my number is 25.
“It’s not a number that fills me with satisfaction, but nor does it embarrass me.”
Lord Darroch, who was National Security Advisor from 2012 to 2015 before becoming Ambassador to Washington, added: “I believe it was a just war.
"And therefore what he has written about, how he justified to himself what he was doing, [I] understand and appreciate that.
“In terms of detail, I personally wouldn’t have gone there.
"But it’s done now.”
The explosive revelation in his book Spare is the first time he has revealed how many deaths in Afghanistan he was responsible for.
His deadly deployment came after he retrained on Apaches in the Army Air Corps, having begun his career as a cavalry officer.
In 2007 the Duke was a forward air controller in Garmsir, southern Helmand, serving with ground forces in an area where Taliban were prevalent.
But his tour of duty was dramatically cut short when an Australian publication breached a media embargo on him being at war.
After learning to fly Apaches he was deployed to Camp Bastion in southern Afghanistan with 662 Squadron Army Air Corps.
Captain Wales qualified as a co-pilot gunner in February 2012 and deployed back to the war zone in September 2012.
The Prince’s two Afghanistan deployments have led to fears he could be attacked by terrorists seeking revenge.
The new book is available for pre-order here.