Queen Elizabeth II wanted both Prince William and Prince Harry to go to war during their service in the military, but it was deemed too dangerous for the Prince of Wales, a former British army head has said. 

"It was decided that William as heir to the heir, the risk is too great," retired British army Gen. Sir Mike Jackson said in an upcoming ITV documentary "The Real Crown: Inside the House of Windsor," according to Sky News. "But for his younger brother, the risk was acceptable."

Jackson said he was breaking protocol in speaking about what was discussed with the late queen about her grandsons’ service. 

"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," he explained. 

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Princes William and Harry in military uniform

Princes William and Harry both served in the military, but only Harry saw combat.  (Max Mumby / Indigo / Getty Images)

"She was very clear — she said, 'My grandsons have taken my shilling, therefore, they must do their duty.' And that was that," he said.

William actively served in the Royal Army, Navy and Air Force for nearly eight years but never saw combat.

Prince William and Prince Harry at Queen's vigil

It was considered too great a risk for Prince William to go to Afghanistan, a retired British general has said. (Aaron Chown)

Harry, on the other hand, served in the British army for 10 years, doing two tours in Afghanistan as a helicopter pilot. 

Military service is traditional for the British royal family

Indeed, the late queen herself served five months in the Auxiliary Territorial Service as a princess during World War II where she trained as a driver and a mechanic, according to the Imperial War Museum.  

Queen Elizabeth with William and Harry

Queen Elizabeth II wanted both Princes William and Harry to go to war, a retired general divulged. (Getty Images)

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Despite the decision, William was "keen" to fight overseas, "unequivocally," Mark Cann, director of the British Forces Foundation, told ITV. 

Prince Harry

Prince Harry did two tours in Afghanistan. (John Stillwell / Pool / Tim Graham Picture Library / Getty Images)

"I think it was really tricky. Anybody who’s in the military who hasn’t actually been on operation feels a sense of disappointment," Cann said of William. "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."

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Similarly, King Charles III, who served in the military, was also reportedly forbidden to see combat when he was first in line to the throne.