The Duke of Cambridge flew a helicopter to a hospital to celebrate the 30th anniversary of London's Air Ambulance.
Prince William, a former pilot with the air ambulance service in East Anglia, flew from Kensington Palace for 25 minutes before landing on a helipad at the Royal London Hospital.
The ceremonial flight marked the duke being named as patron for the charity's anniversary campaign.
A top pilot said he was impressed with the duke's aviation skills.
Neil Jeffers said: "We put him in the right seat, the captain's seat of the aircraft.
"He has only flown the aircraft a couple of times but was happy to fly it - so he did all the flying from the palace."
As part of his visit to the charity, the prince was shown a graphic demonstration of how paramedics would deal with a stab victim.
But, in a lighter moment, he was given a birthday card to pass on to his wife, the Duchess of Cambridge, who turned 37 on Wednesday.
He said: "I did remember this morning - so I was OK."
The card was made by Alma Shahar, six, whose father Yair Shahar, 49, had been given critical treatment by the air ambulance after being run over by a car when cycling in Edmonton, north London, in 2016.
Alma wrote in the card: "Kate, I hope you've had the best birthday you could ever imagine."
Kensington Palace thanked the public for their "lovely messages".