Speaking in a forthcoming ITV documentary called The Real Crown, Sir Mike said: “What goes on in those audiences and who says what to whom remains for the two people involved, and I will break the rule about not divulging what goes on on this one occasion.
“She was very clear. She said, ‘My grandsons have taken my shilling, therefore they must do their duty.’ And that was that. But it was decided that William, as heir to the heir, the risk is too great. But for his younger brother, the risk was acceptable.”
The ITV documentary claims the Queen made the decision after learning of the risks faced by Army personnel fighting the Taliban in Afghanistan through detailed information to which she had access.
Sir John Scarlett, head of MI6 at the time, said: “Of course she has complete clearance to everything. She has complete access to an exceptional amount of info and insight for longer than anyone else. William was very keen to go.
He added: “She’s very, very discreet, completely reliable and completely on top of the detail. I remember thinking at the time, ‘Wow, Her Majesty knows more about this than we do’.”
Prince Harry served in the British Army for 10 years and completed two operational tours of Afghanistan between 2007 and 2013.
He rose to the rank of Captain during his time in the Armed Forces and served as an Apache helicopter co-pilot and gunner.
Prince William, first in line to the throne, completed a training course at the Royal Military Academy Sandhurst and became an Army officer in December 2006. The Prince of Wales served with the Household Cavalry (Blues and Royals) until 2008 and later joined the Royal Air Force and the Navy.
William was eager to serve in Afghanistan and would have been disappointed he could not participate in the conflict, according to Mark Cann, director of the British Forces Foundation.
He told the series: “William was very keen to go. Unequivocally. But it was complex, and some very great minds and experienced people took a view on it.
“I think it was really tricky. Anybody who’s in the military who hasn’t actually been on operation feels a sense of disappointment.
“And I think especially that was the one [war] at the time, you’ve got everyone around you at the time who’s been involved in it. So there is a sense of disappointment.”
The Duke of Sussex has credited his career in the military with saving him after the sudden death of his mother, Diana, Princess of Wales.
“My military career saved me in many regards,” he told CBS in an interview to promote his memoir. “Got me out of the spotlight from the UK press.
“I was able to focus on a purpose larger than myself, to be wearing the same uniform as everybody else, to feel normal for the first time in my life. It felt like I was turning pain into a purpose.”
The full series of The Real Crown: Inside the House of Windsor airs on ITVX on 20 April.