Prince Harry arrived to take part in the biggest gathering of Battle of Britain aircraft since the Second World War to mark the aerial conflict's 75th anniversary - and was admonished within minutes of his inspection of the historic fleet.
Around 40 Spitfires, Hurricanes and Bristol Blenheim bombers will fly in formation from Goodwood Aerodrome in West Sussex this lunchtime before dispersing across wartime airfields over the South of England.
Following a briefing for pilots and those taking part in the flypast, Harry, celebrating his 31st birthday, set off on foot to inspect the aircraft lined up by the grass runway.
But as his group began to cross the runway, a security vehicle came speeding up and stopped the Prince and his group in their tracks.
He could be seen being told to stand back and not cross the runway and a few minutes later a small aircraft came in to land.
Harry was then cleared to cross and continue his inspection as rain poured down on the airfield.
The aerial display will be a tribute to the Second World War pilots famously dubbed "The Few" by wartime prime minister Winston Churchill for their efforts in defeating the Luftwaffe.
During the summer and autumn of 1940, 544 personnel from Fighter Command died as the RAF fought in the skies above southern England to force back the threat of any invasion by Hitler.
The 75th anniversary is likely to be the last major anniversary at which the surviving members of the pivotal conflict - who are now all well into their 90s - will be fit to take part.
Tom Neil, 95, an ex-wing commander and Battle of Britain Hurricane and Spitfire pilot, will lead the formation from the rear of a two-seater Spitfire - the symbol of Britain's fight against Nazi forces.
The event has been organised by the Boultbee Flight Academy, based in Chichester, and two of the aircraft - a Spitfire and a Hurricane - fought in the famous battle.
A royal spokesman said Harry is "incredibly honoured" to be part of the flypast on his birthday.
The Prince will fly in the Spitfire PV202 piloted by John Romain, managing director of the Aircraft Restoration Company at Duxford, Cambridgeshire.