King Charles looked thrilled as gave the royal salute in his first Trooping the Colour since his cancer diagnosis after riding down the Mall in a state carriage with Queen Camilla.
The royal couple were slowly transported, with the monarch saluting as he looked intently out at the gathered guardsmen as the line was presented.
Standing on Horse Guards Parade as they marched past, the King and Queen received the soldiers' salute as the stunning display played out in central London.
Royal fans packed The Mall to show their support for the King after a turbulent year where both he and the Princess of Wales have been forced to step back after being diagnosed with cancer.
Now, in a moment that has thrilled the nation, both have attendde Trooping the Colour in a vibrant celebration of Charles' official birthday in a joyful return to the public eye.
The monarch, 75, broke tradition as attends the ceremony in a carriage rather than on horseback in his latest high-profile appearance.
But, as he sat next to his strength-and-stay, Queen Camilla, 76, the royal pair looked resplendent as they observed the parade.
Riding in the Scottish State Coach in uniform, he regally watched out as the Princess of Wales and her children smiled broadly as they followed behind.
Prince William and the Duke of Edinburgh also joined the parade on horseback, while the Duchess of Edinburgh also travelled along The Mall in a carriage.
King Charles III salutes the gathered guardsmen as the line was presented
King Charles III and Queen Camilla travel along The Mall to the Trooping the Colour ceremony
The Queen looked resplendant in a pale blue outfit and a matching hat, while Kate looked joyful in a white coordinated set
Riding in the Scottish State Coach in uniform, he looked thrilled as he waved to crowds gathered to celebrate his birthday
The monarch, 75, will break tradition as attends the ceremony in a carriage rather than on horseback in his latest high-profile appearance
As he sat next to his strength-and-stay, Queen Camilla, the royal pair looked resplendent as they observed the parade
Britain's King Charles arrives for the Trooping the Colour parade which honours his official birthday
King Charles III and Queen Camilla arrive at Buckingham Palace ahead of the Trooping the Colour ceremony at Horse Guards Parade
King Charles III and Queen Camilla arrive for the Trooping the Colour ceremony to see the gathered ranks of guardsmen
Kate smiled broadly as she looked out at the crowd gathered in the rain in central London
Prince Louis (left) pulls a face at the crowd as Princess Charlotte (right) looks regal as they join the parade
Princess Charlotte grins out at the crowd as she sits next to Prince George at Trooping the Colour on The Mall
Prince George of Wales and Princess Charlotte of Wales wave during Trooping the Colour
Prince William, Prince Edward, and Princess Anne salute on Horse Guards Parade for the King's Birthday Parade
Prince William, Prince of Wales, Prince Edward, Duke of Edinburgh and Princess Anne, Princess Royal perform on Horse Guards Parade
Prince William leads the royals on horseback as he rides infront of the gathered soldiers
The Princess of Wales with Prince William and their three children in London this morning
The Band of the Grenadier Guards march along The Mall towards Horse Guards Parade
A member of the Irish Guards with their mascot Irish wolfhound, Turlough Mor, affectionately known as Seamus, march along The Mall towards Horse Guards Parade
Wearing the tunic of the Guard of Honour Order, the Irish Guards, the monarch saluted the soldiers as he watched from the window.
As per tradition, his uniform bore his predecessor's cypher - that of the Queen.
The Queen looked resplendent in a pale blue outfit and a matching hat, while Kate looked joyful in a white coordinated set.
Beaming from the carriage, she waved to the crowd before taking refuge with her children on a balcony to watch the spectacle from above.
The youngest of the Wales children, Louis, six who is loved by many royal fans thanks to his expressive behaviour, appeared less than thrilled during the ride, at point knitting his brows as he stared out of the window, open-mouthed.
Another snap of the young prince showed him frowning, with his mouth downturned.
Meanwhile, Prince George, 10, appeared typically composed, while Charlotte, nine, was snapped beaming as she looked out of the carriage window at the assembled crowds.
Among the crowd, Prime Minister Rishi Sunak and his wife Akshata Murty had a front row seat.
Scotland Yard has a 'substantial' policing operation for the event, with anti-monarchy group Republic allowed to protest but banned from using amplified sound.
In a post on X today, Republic said: 'It's a lovely sunny day (so far) for a protest! Join us, outside Buckingham Palace from 9.00am. #NotMyKing #AbolishTheMonarchy.' As the king arrived by car the group booed.
Hundreds of Metropolitan Police officers will be deployed on the ceremonial route to ensure the safety and security of attendees, with tens of thousands expected.
Organisers have advised the public to stand on The Mall or on the edge of St James's Park overlooking Horse Guards Parade from 9am, with the parade starting at 10am. Coverage on BBC One begins at 10.30am and concludes after the flypast at 1pm.
Another snap of the popular young Prince showed him grimacing as he rode to Buckingham Palace
Prince George, Princess Charlotte, Prince Louis and Kate at Trooping The Colour today
The Princess of Wales speaks with Prince Louis as they watch Trooping the Colour today
The Prince and Princess of Wales arrive at Buckingham Palace in London this morning
The Duchess of Edinburgh travels along The Mall to the Trooping the Colour ceremony
Members of the Irish Guards march along The Mall towards Horse Guards Parade today
George sits between his mother Kate and father Prince William in the car in London today
The Princess of Wales arrives at Buckingham Palace in London this morning
Princess Charlotte looks out the window as the family arrive at Buckingham Palace today
The Prince and Princess of Wales arrive at Buckingham Palace in London this morning
Prime Minister Rishi Sunak and his wife Akshata Murty attend the King's Birthday Parade
Last week the King appeared at a D-Day event in Portsmouth to give his first public speech and most high-profile appearance since his cancer diagnosis.
A day later he travelled overseas for the first time as he expressed his 'profound sense of gratitude' for the men and woman 'who did not flinch when the moment came to face that test.'
He has now followed the late Queen in his decision to opt to use a carriage rather than riding as he inspects the troops formed up in Horse Guards Parade.
The Scottish State Coach is well-equipped to brave out the rain - as an enclosed, four-horse-drawn coach originally built in 1830 and previously used to transport Princess Eugenie and Jack Brooksbank on their wedding day.
Last year grooms had to step in after he became the first monarch since the late Queen in 1986 to saddle up for the parade.
Noble, a black mare gifted to Charles by the Royal Canadian Mounted Police when he became King, struggled to adapt to the surroundings and they had to step forward to help steady the horse.
Royal fans lining The Mall were also left thrilled today as they saw the Princess of Wales for the first time in public since she revealed she had been receiving treatment for an undisclosed form of cancer since late February.
Yesterday, she confirmed she will ride in a carriage alongside her three children, Prince George, Princess Charlotte and Prince Louis, for the traditional procession through London.
Royal fans try to take cover from the rain ahead of Trooping the Colour in London today
Republic protesters hold up placards on The Mall ahead of Trooping the Colour this morning
Protesters and royal fans hold umbrellas on the The Mall before Trooping the Colour today
Royal fans stand on The Mall in London ahead of Trooping the Colour this morning
Members of the public gather on The Mall ahead of Trooping the Colour this morning
Later, she is expected to gather with King Charles and Queen Camilla, her husband Prince William and other royals on Buckingham Palace's balcony for the RAF flypast.
A Palace spokesperson said: 'His Majesty is delighted that the princess is able to attend tomorrow's events, and is much looking forward to all elements of the day'.
William spent a number of weeks with Kate and their children during the Easter holidays before returning to public work in mid-April.
Charles was admitted to hospital just days after Kate, also for a procedure deemed unrelated to cancer.
In February, Buckingham Palace confirmed that he had been diagnosed with a form of cancer, which is not prostate cancer, that was discovered while the King was being treated at the private London Clinic for an enlarged prostate.
In wishing the monarch a full recovery, Prime Minister Rishi Sunak said thankfully the cancer had been 'caught early'.
Charles initially postponed public-facing duties but resumed at the end of April, speaking of his 'shock' at being diagnosed with cancer as he met patients on a visit to University College Hospital Macmillan Cancer Centre in central London.
The Queen provided an update on her husband's health at the Queen's Reading Room Literary Festival at Hampton Court Palace in Surrey last Saturday, telling author Lee Child the King is 'doing fine' but 'won't slow down and won't do what he's told'.
Royal fans stand on The Mall in London ahead of Trooping the Colour this morning
Royal fans try to take cover from the rain ahead of Trooping the Colour in London today
Protesters and royal fans hold umbrellas on the The Mall before Trooping the Colour today
Royal fans stand on The Mall in London ahead of Trooping the Colour this morning
Royal fans on the The Mall in London this morning ahead of the Trooping the Colour ceremony
Protesters and royal fans hold umbrellas on the The Mall before Trooping the Colour today
The Mail revealed in March that Charles would potentially have to use a carriage to attend the ceremonial event following his cancer diagnosis in February.
It was reported that the monarch, though determined to attend the event despite ongoing treatment for the illness, might have to watch the military spectacular from a podium instead of on horseback as usual, having been driven from Buckingham Palace in a carriage as his late mother used to.
Despite being an accomplished polo player in his younger years, it has been reported that the King does not ride for enjoyment any more.
Dating from the 17th century, Trooping the Colour is one the biggest military ceremonial events of the year, involving more than 1,200 soldiers and musicians plus more than 200 horses.
Usually the monarch rides down from Buckingham Palace to Horse Guards Parade via The Mall to inspect the troops.
The sovereign then rides back to the palace for the traditional balcony appearance with the wider Royal Family and flypast by the RAF.
Charles first attended the ceremony in 1951, aged just two, when his mother took the place of King George VI, who was too unwell to attend.
From 1987, when her horse Burmese retired, the late Queen chose to travel to the event by carriage.