Prince Harry Wales
Prince Harry was promoted to Army Air Corps Captain after five years of serving in the British Armed Forces. He is is seen posing for a photograph in a Squirrel helicopter at RAF (Royal Air Force) Shawbury near Shrewsbury, England, in this June 10, 2009. REUTERS/Ian Forshaw/MOD/Handou

It has been revealed that Queen Elizabeth II initially wanted both her grandsons to serve their country and go to war but decided on having Prince Harry go alone instead because the risk was too great for Prince William.

In the upcoming ITV documentary, "The Real Crown: Inside the House of Windsor," former British Army general Sir Mike Jackson recalled a conversation he had with the late monarch about the princes.

He revealed that the chiefs normally have an "audience with The Queen once or twice a year" and during these meetings, it was advisable that they come prepared. He said, "You need to have done your homework. She's very wise."

Jackson shared, "I used to tell my staff, see if you can get the midday slot. Um, because after half an hour or 40 minutes, the Queen would ring a small bell and 'Time for a Sherry, I think, CGS'."

He added, "What goes on in those audiences and who says what to whom, remains for the two people involved. And I will break the rule, uh, about not divulging what goes on on this one occasion when she was very clear — she said, 'My grandsons have taken my shilling, therefore they must do their duty.' And that was that."

However, Queen Elizabeth II eventually decided against sending Prince William to war because according to Jackson, the risk was "too great" for him given that he is second in line to the throne. But the "risk was acceptable" for Prince Harry, who is currently fifth in the royal line of succession.

But Prince William "was very keen to go" to war in Afghanistan according to Mark Cann, director of the British Forces Foundation. He said, "Unequivocally. But it was complex, and some very great minds and experienced people took a view on it."

He continued, "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."

According to People, Prince William spent over seven years in full-time military service, three years as a search and rescue helicopter pilot before he retrained as a pilot with the East Anglian Air Ambulance. He was also with the Royal Air Force and the Royal Navy.

Meanwhile, Prince Harry served ten years in the British Armed Forces and fought in the war in Afghanistan twice. He talked about his years in the army and his deployment in his memoir "Spare," admitting that he killed 25 Taliban soldiers and likened them to chess pieces being removed from the board.

Following his years in the army, the Duke of Sussex launched the Invictus Games, an international multi-sport event for the "wounded, injured and sick servicemen and women, both serving and veterans."

Prince Harry called his years in the Armed Forces "a duty, a job and a service" to his country saying that he has done all he could "to be the best soldier" he was trained to be. He also talked about how keeping silent about his experiences in the war "has been the least effective remedy" and instead chose to express and detail them "in the hopes it would help others." He told the magazine in an exclusive interview about "Spare," "I don't know that you ever fully reconcile the painful elements of being at war. This is something each soldier has to confront, and in the nearly two decades of working alongside service personnel and veterans, I've listened to their stories and have shared mine."