The royal family celebrated the King's birthday parade, known as Trooping the Colour, with the Princess of Wales making her first public appearance this year on Saturday.
The crowds cheered and applauded as Kate, 42, who has been receiving treatment for an undisclosed form of cancer since late February, was joined by her three children, Prince George, Princess Charlotte and Prince Louis, in a carriage for the traditional procession.
She was surrounded by other members of the family, with her husband the Prince of Wales, Colonel of the Welsh Guards, on horseback, as were the Princess Royal, Colonel Blues and Royals, and the Duke of Edinburgh, Colonel Scots Guards.
And in another change, the King, 75, travelled in a carriage with his wife, Queen Camilla, 76, instead of riding horseback amid his ongoing cancer treatment.
Meanwhile, the Duchess of Edinburgh was accompanied by her daughter, Lady Louise Windsor, 20, and the late Queen Elizabeth's cousin, the Duke of Kent.
The impressive display of pageantry at Horse Guards Parade saw over 1,400 officers and soldiers form the parade, together with two hundred horses. Meanwhile, over four hundred musicians from ten bands and Corps of Drums marched and played in unison.
Despite the torrential rain, the royals were in high spirits as they made their way back to Buckingham Palace in their carriages, with George, Charlotte and Louis waving enthusiastically to the crowds. Six-year-old Louis also made mum Kate giggle with his dancing during the ceremony.
Ahead of her appearance, the Princess shared a personal update about her progress in a letter released on Friday, she wrote: "I'm looking forward to attending the King’s Birthday Parade this weekend with my family and hope to join a few public engagements over the summer, but equally knowing I am not out of the woods yet."
Meanwhile, a spokesperson for Buckingham Palace 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."
The Prince and Princess of Wales also shared an incredibly moving video of Kate and their children waiting for their carriage at the palace, with the Princess tenderly playing with her daughter Charlotte's hair.
See all the best photographs and moments from the day...
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© GettyEarly start
Fans began gathering down The Mall in the early hours of the morning to take their places for the procession.
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© GettyRoyal watchers
Many fans carried flags and dressed up in red, white and blue outfits.
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© GettyPreparations
Royal household staff were pictured preparing the famous Buckingham Palace balcony ahead of the flypast.
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© GettyBalcony
Staff prepared the balcony with the iconic red and gold drapes. The royal family will gather together to watch the military spectacle after the procession.
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© GettyThe Wales family arrive
The Prince and Princess of Wales were pictured arriving at Buckingham Palace by car with their children.
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© GettyFirst sighting of Kate
Kate wore a white dress with black bow detailing by one of her go-to British designers, Jenny Packham, and a wide-brim saucer-style hat by Philip Treacy.
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© James WhatlingThe Princess wore pearl earrings with her ensemble and her Irish Guards Regimental Brooch.
Kate is Colonel-in-Chief of the regiment and wrote a heartfelt apology letter as she was unable to take the salute at the Colonel's Review on 8 June ahead of Trooping the Colour.
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© GettyThe Duke and Duchess of Edinburgh were pictured travelling in a car with daughter, Lady Louise Windsor, who was last seen at the Royal Windsor Horse Show in May.
Sophie looked lovely in a yellow ensemble while Edward donned military uniform.
Lady Louise, 20, rewore her floral Suzannah London silk dress from King Charles' coronation.
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© ShutterstockPrince Louis
William and Kate's youngest child peeked at the crowds from the car. Louis, who turned six in April, always manages to steal the show at major royal events.
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© GettyLady Louise Windsor
Lady Louise braved the rain to wave to the crowds as she shared a carriage with her mother and the Duke of Kent.
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© GettyThe King and Queen
In a change from last year, the King travelled in the procession by carriage.
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© GettyAll smiles
The Princess beamed and waved at the crowds as she shared a carriage with George, Charlotte and Louis, as they made their way down The Mall.
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© GettyRiding horseback
William, Edward and Anne rode down The Mall to Horse Guards Parade on horseback.
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© GettyLovely in lemon
The Duchess of Edinburgh looked beautiful in a lemon Beulah London dress with flared sleeves and button detailing around the waistline.
Sophie waved from the carriage alongside the late Queen's cousin, the Duke of Kent.
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© Chris JacksonPrincess Charlotte
Princess Charlotte, nine, wore a navy sailor-style dress with white piping and a matching bow in her hair.
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© GettyNautical twinning
Royal mum and daughter Kate and Charlotte had a matching moment in nautical-style white and navy outfits with similar shoes as they exited the carriage to watch the ceremony from the Major General's Office at Horse Guards Parade.
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© GettyMaking their way
The King and Queen travelled in an Ascot Landau carriage.
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© Jonathan Brady - PA ImagesQueen Camilla
Her Majesty opted for a pale green silk crepe dress and coat from Anna Valentine and hat by Philip Treacy, finished with her Grenadier Guards military brooch.
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© GettyRoyal salute
The Prince of Wales, the Duke of Edinburgh and the Princess Royal were pictured saluting the troops during the ceremony.
Prince William wore the Full Ceremonial Guard Order of the Welsh Guards, as he is colonel of the regiment.
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© GettyRoyal wave
We love this stunning photograph of the Duchess of Edinburgh during the carriage procession.
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© BBCFront row seats
Kate and her children watched the proceedings from the Major General's Office, with Louis, dressed in a military jacket, taking a particular interest.
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© ShutterstockRoyal brothers
Prince George, ten, and Prince Louis, six, matched in navy suits with blue ties. Louis sported shorts as tradition for royal children under eight.
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© GettyBack to the palace
After the ceremony, the royals travelled back to Buckingham Palace in their carriages, with Lady Louise this time taking shelter under cover from the torrential rain with Sophie and the Duke of Kent.
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© GettyCaught in the rain
A striking close-up shot of William in the rain during the ceremony.
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© GettyThe grand finale
The royals gathered on the Buckingham Palace balcony to watch the spectacular flypast from the Royal Air Force.
It ended with the red arrows trailing their trademark red, white and blue colours.
The Prince and Princess of Wales smiled and spoke with their children on the balcony of Buckingham Palace as the planes roared overhead.
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© GettySlimmed down balcony
In recent years only senior working royals have appeared on the balcony for major royal moments, in a departure from Queen Elizabeth II's reign when she would invite extended members of her family.
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© GettyFamily moment
William and Kate beamed at Louis as he gazed at the aircraft in awe.
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© GettyThe look of love
William and Kate were spotted exchanging loving glances. The pair celebrated their 13th wedding anniversary in April.
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© GettyPretty in pastels
Queen Camilla and Duchess Sophie shared a sweet moment on the balcony
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© GettyAltogether
The Edinburghs stood alongside the Princess Royal to watch the flypast.
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© GettyRed Arrows
The Red Arrows trailed their iconic red, white and blue colours as the flypast concluded.
