A new documentary claims the late Queen authorised her grandsons, the Prince of Wales and Duke of Sussex, to fight in Afghanistan saying “my grandsons have taken my shilling, therefore they must do their duty”.

In a five-part ITV series chronicling the royal family, General Sir Mike Jackson reveals Queen Elizabeth’s comments but says since Prince William is future king, so it was decided he wouldn’t serve on the front line.

The Real Crown: Inside The House Of Windsor features interviews with contemporary figures and will be available to watch in full from April 20.

In the final documentary episode, General Sir Mike Jackson, who served as Chief of the General Staff (CGS) from 2003-06, says: “The chiefs have an audience with the Queen once or twice a year. You need to have done your homework.

“She’s very wise. I used to tell my staff, see if you can get the midday slot because after half an hour or 40 minutes the Queen would ring a small bell and ‘Time for a sherry I think, CGS’. ‘Very good idea, ma’am’.

“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 when 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 for William as heir to the heir, the risk is too great. But for his younger brother, the risk was acceptable.”

What job did Prince Harry do in the army?

When Sir Mike was head of the army, Harry was an army officer while William was an officer cadet.

Harry went on to serve two tours in Afghanistan where UK forces were part of a multi-national operation fighting the Taliban insurgency.

Bournemouth Echo: Harry served two tours of Afghanistan during his time in the armyHarry served two tours of Afghanistan during his time in the army (Image: PA Wire/PA Images)

In his first tour, during 2007-08, Harry worked as a forward air controller co-ordinating air strikes on Taliban positions.

His tour of duty was abruptly ended when foreign websites broke a media blackout on reporting details of his service.

Harry retrained as a helicopter pilot and was deployed back to the front, serving as an Apache helicopter co-pilot gunner during 2012-13.

William served as an RAF search and rescue helicopter pilot but was not deployed into an active combat zone, unlike his uncle the Duke of York.

At age 22, Andrew saw active service in the Royal Navy as a Sea King helicopter pilot in the Falklands War in 1982.

His service included flying his aircraft as a decoy target, trying to divert deadly Exocet missiles away from British ships.