"There is a lot of banter between them because of them both being helicopter pilots," says a royal source.
"Prince Harry tells Prince William he is flying a washing machine, because the Sea King is such an old, reliable workhorse, and William tells Harry he is flying a computer game because the Apache is so sleek, fast and advanced."
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The end of the course means Captain Wales, as Harry is known in the Army, is now eligible to be deployed in Afghanistan.
On a visit to RAF Honington in Suffolk, he chatted to fellow servicemen and their families about preparing for duty.
Harry, who'd been asked to hand out commendations in his capacity as Honorary Air Commandant of the base, spoke of his "nightmares" about forgetting his kit when on tour.
Corporal Owen, 29, from Shrophire, said: "He was saying, because there's a lot of kit nowadays, you've got to remember so much.
''He said it was bringing back nightmares about all the stuff you have got to remember.''
Meanwhile, Senior Aircraftman Josh Brown described him as "just an average sort of bloke" and said they chatted about the "pizzas and burgers and KFC" you can get in Camp Bastion, where the Prince previously served.
Earlier this week, the Top Gun royal was presented with an award for his shooting skills.
The 27-year-old received a trophy – a poilshed 30mm round from from an Apache cannon mounted on a stand – for being the best co-pilot gunner.
It was given to him at a dinner on Wednesday night at Wattisam Air station, near Honington, to mark the end of 18 months of training.
A spokesman for Prince Charles, who also trained as a helicopter pilot, said he was "very proud of his son's achievement".
With Harry returning to Afghanistan – as part of 662 Squadron, 3 Regiment Army Corps – as a co-pilot and gunner, there are now two members of the Royal family deployed on operational service for the first time ever.
William has been on duty with 22 Squadron in Anglesey, Wales, since August 2010.