King Charles III received the official birthday wishes of the nation in the first Trooping the Colour of his reign on Saturday.
Pomp and pageantry were on full display as thousands of people lined The Mall in central London to watch the monarch, 74, take the salute from soldiers.
After the parade, the king's grandchildren, Prince George, Princess Charlotte and Prince Louis, joined other members of the royal family on the Buckingham Palace balcony to watch a flypast, which included a surprise tribute spelling out the monarch's initials, CR.
The well-choreographed event marked the first official birthday of his reign in a tradition dating back more than 260 years.
The king was joined on horseback by the royal colonels – the Prince of Wales, Colonel, Welsh Guards; the Princess Royal, Gold Stick in Waiting and Colonel of The Blues and Royals; and the Duke of Edinburgh, riding for the first time in his role as Colonel of the 1st Battalion London Guards, formed last year.
Travelling in a carriage behind were Queen Camilla, who is Colonel of the Grenadier Guards, and the Princess of Wales as Colonel of the Irish Guards, along with Prince George, nine, Princess Charlotte, eight, and five-year-old Prince Louis.
The royal party were in the midst of a sovereign's mounted escort, formed by troops from the Household Cavalry's Life Guards and Blues and Royals, wearing shining breastplates and plumed helmets.
Cheers followed them as they travelled along The Mall.
Julia Walker, from Hampshire, was among the first to arrive at The Mall yesterday afternoon to take a prime spot to see the king.
"I am a real royalist, so it doesn't take much for me to come to The Mall and enjoy it," she told The National.
"I have seen [Trooping the Colour] twice and many years ago, in 1977 for the Silver Jubilee, because she (Queen Elizabeth II) rode side saddle. And then I saw it many years again later."
It is the fourth royal event Ms Walker has been to in the past year, after the Platinum Jubilee celebrations, Queen Elizabeth's funeral and the coronation of the king in May.
"I thought I might as well do the whole experience to do his first Trooping the Colour. So I thought I would come early to this, and here I am."
The event involved about 1,500 soldiers in total and hundreds of Guardsmen were lined up on the parade ground waiting to be inspected by king, who will be joined by the mounted royal colonels, including the queen and Kate in a carriage.
For the first time since 1989, all five regiments of Foot Guards – the Welsh, Scots, Irish, Coldstream and Grenadier – were on parade together for Trooping The Colour.
The colour, or regimental flag, paraded in front of hundreds of guardsmen and officers was the King's Colour of the 1st Battalion Welsh Guards.
Among the guests was Prime Minister Rishi Sunak, Sophie, Duchess of Edinburgh, Vice Admiral Sir Tim Laurence and senior military figures.
The king later returned to Buckingham Palace to watch a six-minute ceremonial flypast.
First Trooping the Colour of King Charles III - in pictures
Thousands filled The Mall after the Trooping the Colour ceremony ended and greeted the king with cheers and applause as he led members of the royal family onto the balcony of Buckingham Palace.
Charles was joined by the Prince and Princess of Wales, their children and other family members as he acknowledged the spectators with a wave.
A few seconds later the first element of the extended fly-past - a contingent of helicopters - thundered overhead.
One of the highlights of the flypast above Buckingham Palace saw 18 Typhoon fighter jets spelling out the King's monogram "CR" for Charles Rex.
But all eyes were on the king's five-year-old grandson, Louis, who rose to the occasion by saluting during the traditional flypast and seemed to pretend to ride a motorcycle or bike with his arms outstretched.
Another was the sight of aircraft associated with the Second World War, with Spitfire and Hurricane fighters flying with a Lancaster bomber, all from the Battle of Britain Memorial Flight.
As the planes roared overhead Kate encouraged Prince George to wave to the crowds and she smoothed down Prince Louis' hair and ushered him to turn and face the spectators.
The finale was precision formation flying from the Red Arrows who trailed red, white and blue smoke over the capital.
The display, which featured 70 aircraft from the Royal Navy, army and Royal Air Force, was extended to make up for the flypast on coronation day being scaled down because of bad weather.
The aircraft took off from15 locations before meeting in the south-east of England to fly across London.
Trooping the Colour celebrates the sovereign's official birthday, a custom started by German-born King George II in 1748, who wanted a summer celebration because his birthday was on October 30.
The present king's birthday is on November 14.
The king, Princess Anne and heir to the throne Prince William all rode at last year's event, which formed part of four days of celebrations for the late queen's platinum jubilee, marking her 70th year on the throne.
It was one of her last public appearances before her death in September, aged 96.
Before Saturday, Queen Elizabeth was the last monarch to ride at the event, in 1986, with her favourite steed, a black mare called Burmese, for the 18th and final time in the annual ceremony before the mare was taken to Windsor for retirement.
Rather than train another horse for the ceremony the queen decided to be driven in a carriage.
Her decision came five years after a man fired blank shots at her while she was riding along The Mall on Burmese.
The former Royal Canadian Mounted Police horse began to rear in fright but the queen, an accomplished equestrian, brought the horse back under control.
The man, Marcus Sarjeant, was sentenced to five years in jail.
