The King praised the Prince of Wales, calling him a "very good pilot" as he handed over his former military role to his son and heir.
Prince William, 41, officially became Colonel-in-Chief of the Army Air Corps as he joined his father, Charles, 75, at the handover ceremony at Middle Wallop in Hampshire on Monday.
The King, who was welcomed by a Guard of Honour after arriving at the Army Aviation Centre via helicopter, toured the Army Flying Museum, where he delivered a touching speech, which you can watch in full below…
WATCH: King Charles praises son Prince William during joint outing "I did just want to say what a great joy it is to be with you even briefly on this occasion," Charles began. "But also tinged with great sadness after 32 years of knowing you all and admiring all your many activities and your achievements throughout the time, I've been lucky enough to be Colonel-in-Chief of the Army Air Corps."
He added: "So all I can say is that having had the pleasure of knowing you for so long, I do hope you'll go from strength to strength in the future with the Prince of Wales as your new Colonel-in-Chief. The great thing is he's a very good pilot indeed so that's encouraging. So ladies and gentlemen, look after yourselves and, and, and I can't tell you how proud it has made me to be involved with you all this time."
The Army Air Corps is the Duke of Sussex's old unit, in which he served as an Apache helicopter commander and co-pilot gunner during his second tour to Afghanistan in 2012. The King's decision to hand the role to William was seen as a blow to Harry when it was announced last year.
See all the best photos from William and Charles' joint outing as it happened...
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Father and son sharing a laugh as they arrive
The King and the Prince of Wales were spotted sharing a chuckle as William arrived at the airfield for the handover ceremony. The new military appointment was announced last August, with Charles handing over the role after 32 years.
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Charles and William during the official handover
The father and son posed for photographs in front of an Apache helicopter for the official handover. William served in the Army with the Blues and Royals and as an RAF search and rescue pilot.
Three years as a search and rescue pilot saw him conduct 156 operations, take on routine operational deployment to the Falkland Islands and qualify as an operational Captain.
After leaving the Armed Forces, William retrained to become an air ambulance pilot and worked with the East Anglian Air Ambulance for more than two years from March 2015.
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Charles and William sported matching ties
It was also announced last August that William has taken on the roles of Colonel-in-Chief of the Mercian Regiment and Royal Honorary Air Commodore of RAF Valley.
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The King handed William the regiment's beret and stable belt in front of the Apache before speaking to serving aircrew.
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The King meeting members of the Army Air Corps
The King, as Sovereign, is Head of the Armed Forces. His Majesty is a military veteran himself, having trained and served in both the Royal Navy and the Royal Air Force.
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The King and Prince of Wales pose for a group photograph with service personnel
Before the King departed and the Prince of Wales carried out his first engagement with the regiment, there was time for a group photograph.
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Charles spoke to local schoolchildren
Earlier in the day, as Charles arrived at the airfield, he went on an impromptu walkabout to greet some schoolchildren from Middle Wallop School, who were gathered waving Union flags. Asked if their parents are part of the regiment, he was told that 60 to 70 percent are.
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The King unveiling a plaque at the Army Aviation Centre
The King delivered a moving speech before unveiling a plaque commemorating an Apache AH Mk.1 going on display, the first of its kind to be installed at a UK museum.
"All that time on operations in Iraq and Afghanistan, I watched with them again, immense admiration for what you did and managed to do out there," Charles said. "And of course, with this remarkable Apache, I remember, I think I probably was taken up with one of these ones all those years ago and I shall never forget it.
"Nor will I forget the fact that when I first became Colonel-in-Chief, you still had quite a few fix me aircraft, one or two, which I flew in along with some rather ancient helicopters."
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William wearing the Army Air Corps uniform and beret
William wore the regiment's uniform as he carried out his first-ever engagement with the Army Air Corps in his new role as its Colonel-in-Chief.
The Prince first received a briefing on the Army Air Corps' current work from the Colonel Commandant, Lieutenant General Sir Nicholas Borton.
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William carried out his first engagement with the regiment
He also inspected training and operational aircraft as well as talking to soldiers.
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William standing in front of an Apache helicopter
William was presented with gifts on behalf of the corps – a tartan scarf for the prince, a wrap for his wife Kate and three wooden helicopter models for each of the couple's children.
Prince William prepares to fly in an Apache helicopter
After his engagement, William left the base in an Apache as part of a capability flight.
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A 17-year-old William leaning against a helicopter in 1999
Ahead of his outing, Kensington Palace posted two images of the Prince during his military service on X, showing a young William in 1998 and 2009 – standing next to a helicopter in one picture and smiling at the controls in another.
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Prince of Wales on the flight deck of a helicopter during a visit to the Army Air Corps in 2008
"Time flies!" the caption read.
LISTEN: King Charles and Prince William declined personal invite sent by Prince Harry
