Royal brothers in arms: first double portrait of Princes William and Harry unveiled at gallery

He has his mother's high cheekbones as well as the Harry Potter golf club scar. The other one has the gingery quiff and … hang on, a broken nose. Definitely a previously unreported broken nose on the man third in line to the throne. The unmistakably battered profile of Prince Harry was revealed as the National Portrait Gallery yesterday unveiled its latest commission: the first double portrait of Prince William and his younger brother, as painted by artist Nicky Philipps. It might best be described as military-casual. The pair are captured in relaxed conversation, dressed in formal Household Cavalry parade uniforms as if about to take part in the trooping the colour ceremony for the Queen's birthday celebrations of June 2008. Philipps, whose best-known previous commission is the writer Ken Follett, was chosen after the NPG interviewed artists it had shortlisted for the job. "I was massively lucky to get the commission," she said. "I remember getting the call and afterwards sitting there thinking, this is so exciting, I can't believe it, but followed quite quickly by, 'I've got to do it. It's all very well getting it but now I have got to make it work'." The princes came to her south Kensington studio for five 90-minute sittings. "They were lovely. Very patient. Very obliging, and I hope they enjoyed it. When they were together they just chatted away between each other when I didn't need them to do something specific." Philipps said she used William's cheekbones as one of her starting points. "He has his mother's high cheekbones and actually that dictated the portrait really. I liked that view of him and from that point onwards I built the rest of it using the poses they had fallen into quite instinctively. And I'm quite glad I had Harry's profile. He has a rather wonderful nose, even though it's broken." Also visible is the scar on William's forehead – whacked accidentally with a seven iron as a child – which the prince last year called his "Harry Potter" scar because it glows after he plays sport. It is understood that Harry broke his nose on the playing fields of Eton – in a rugby match, aged about 16. Philipps said she wanted to capture the brotherly banter that went on – banter she insisted she had been too busy to listen to. "You've got a lot to think about and a lot to do," she said. She knew from the start that Harry should be perched on something and once he did that the poses came naturally. "In the first sitting they were together and they just chatted away. I wanted to just capture what was there in front of me, to be honest. I didn't want any sense of overbearing formality because they are still young and William hasn't got to his role yet. They are army officers as much as anything else and, of course, they're brothers." The NPG's director, Sandy Nairne, said: "What Nicky has done so well is to have them in formal dress but very informally positioned. Nicky has extended the tradition of royal portraiture to make it very informal, and they are chatting as if at Clarence House." The setting of Clarence House, which Philipps visited for research, allowed her to incorporate associations with the Queen Mother. The paintings in the background over William's shoulder – Augustus John's portrait of George Bernard Shaw and a landscape of New Haven by Duncan Grant – were both owned by her. It was the NPG's decision to have the brothers, now aged 27 and 25, in their Blues and Royals lieutenants' uniforms. The NPG said the princes saw the portrait before Christmas and were pleased. It will be displayed publicly for six months in a small exhibition of other royal portraits.