Colonel Tim Collins, known for a pre-battle speech he made in Iraq, said Harry’s conduct is “not how we behave in the army”.
It comes as the duke faces an intense backlash after writing about his time in Afghanistan in his controversial memoir, Spare.
Harry wrote that flying six missions during his second tour of duty on the front line in 2012 to 2013 resulted in “the taking of human lives”, of which he was neither proud nor ashamed.
The Telegraph, which obtained a Spanish language copy of the memoir from a bookshop in Spain, reports that Harry said he did not think of those he killed as “people”, but instead as “chess pieces” that had been taken off the board.
“So, my number is 25. It’s not a number that fills me with satisfaction, but nor does it embarrass me,” he wrote.
But Col Collins is among those in the military community condemning Harry, calling revelations in the book “a tragic money-making scam”.
He told Forces News on Friday: “Amongst his assertions is a claim that he killed 25 people in Afghanistan.
“That’s not how you behave in the army; it’s not how we think.”
Col Collins later added: “Harry has now turned against the other family, the military, that once embraced him, having trashed his birth family.”
He also accused Harry of taking a path that is “alien” to those in the UK and the Commonwealth, adding that the duke is “pursuing US identity politics and casting slurs or racism around where none exists”.
“I wonder whose path he has chosen? In the end I see only disappointment and misery in his pursuit of riches he does not need and his rejection of family and comradely love that he badly needs,” he said.
Lord Kim Darroch, former National Security Adviser, also told Sky News on Friday that “he would have advised against” Harry offering such details about his service in Afghanistan.
Lord Darroch said he “slightly” shared the security concerns military experts have raised after Harry’s comments.
“You have to respect all of those who fought in Afghanistan,” he said.
“I went there a number of times when I was National Security Adviser. It’s a really tough environment, it was a really dangerous war, we lost more than 500 British servicemen.
“I respect and appreciate all those who fought there.
“Personally if I’d been advising the prince, I would have advised against the kind of detail that he goes into there.
“But it’s out there now and I believe it was a just war and therefore what he has written about how he justified to himself what he was doing, I can understand and appreciate that.
“In terms of the detail, I personally wouldn’t have gone there, but it’s done now.”
Meanwhile, Ben McBean, who lost an arm and a leg serving with the Royal Marines in Afghanistan in 2008 and was described by Harry as a “real hero” after they met at several events, told the duke to “shut up”.
He tweeted: “Love you #PrinceHarry but you need to shut up! Makes you wonder the people he’s hanging around with.
“If it was good people somebody by now would have told him to stop.”
A Ministry of Defence spokesperson said they do not comment on operational details for “security reasons”.
Harry was previously criticised in early 2013 when he revealed to the media that he had killed during his tour.
The then-28-year-old told the media that he took the enemy “out of the game”, and soldiers “take a life to save a life”.
“Take a life to save a life,” he shrugged and said during an interview in 2013. “That’s what we revolve around, I suppose.