Harry cradled the tot, who fittingly sported a T-shirt reading 'I am an Invictus baby', while Prince William held onto the infant's tiny hand.
The royal brothers met the adorable newborn when they paid a surprise visit to those trying out for the forthcoming sporting competition.
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Ⓒ: Roger Keller / Help For Heroes
William and Harry were snapped chatting and laughing with potential competitors as they showed off their skills in the hope of taking part when the games kick off on 10 September.
The Invictus Games' official Twitter account announced the royals siblings' unexpected appearance.
"Surprising our #InvictusGames Athletes, the Duke of Cambridge & Prince Harry attend trial," posted the account.
Prince Harry has been busy promoting the tournament over the past couple of weeks.
Speaking to BBC Radio 2 DJ Chris Evans, Harry admitted that the initial concept for the games wasn't his idea, but that he "stole" it from the Warrior Games in America.
"[I was] happy to steal it off the Americans I think, is probably the best way of explaining it," he said. "The Americans have had the Warrior Games now for the last four and a half, five years.
"They have the Navy against the R.A.F. against the Army," he added. "We went over there, I had a team of 30 UK guys that joined in with the Americans and basically saw this event take place and decided that it was such a wonderful concept we should steal it, make it bigger, make it better and bring it back home."