The Princess of Wales beamed as she made a spectacular return to public life today while she continues to receive chemotherapy.

In her first public appearance in 173 days, Kate, 42, looked happy and in good health as she joined her children and senior members of the Royal Family to celebrate the King’s official birthday.

And in a sweet gesture, Charles and his beloved daughter-in-law stood side-by-side in a symbol of strength and unity, as last year the Prince of Wales was positioned next to his father.

Both Kate and the King were diagnosed with cancer at the start of the year and have grown closer as they support each other through this difficult period.

The princess spoke to her father-in-law personally to let him know that she would be attending Trooping the Colour – her first public appearance since Christmas – and he was “delighted” by the news.

Pictures showed the Princess of Wales arriving at Buckingham Palace with her three children, Prince George, 10, Princess Charlotte, nine, and Prince Louis, six, ahead of the King’s birthday parade.

Wearing a crisp white Jenny Packham dress with black details and a hat by Philip Treacy, Kate gazed out of the car window less than 24 hours after she shared a deeply moving message about her ongoing cancer treatment.

It wasn’t long before they appeared from the famous residence in the glass state coach to deafening cheers and cries from the crowds in The Mall.

Kate showed no sign of nerves as she travelled along one of London’s most famous thoroughfares, smiling and waving to those gathered and keeping an eye on her brood.

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.

The King also rode in a carriage with the Queen, as he was unable to participate on horseback because of his illness.

But if he was annoyed by the change it didn’t show, as he waved at the crowds while travelling to Horse Guards Parade.

Their Majesties were preceded by the Duke and Duchess of Gloucester and Vice Admiral Sir Tim Laurence’s carriage, while the Duchess of Edinburgh travelled in a coach with her daughter Lady Louise Mountbatten-Windsor and the Duke of Kent.

Charles is Colonel in Chief of the regiments of the Household Division which include the Life Guards, Blues and Royals and all five regiments of Foot Guards – the Welsh, Scots, Irish, Coldstream and Grenadier – on parade for the official birthday, alongside the mounted Band of the Household Cavalry and the massed Foot Guards bands.

When the inspection of the Guardsmen in their scarlet tunics and bearskins began, the King cast his eye over the servicemen who are fighting soldiers when not performing ceremonial duties.

Sat beside him in the carriage was the Queen who wore a pale green silk crepe dress and coat by Anna Valentine, Philip Treacy hat and her Grenadier Guards military brooch.

The Princess of Wales looked happy and healthy (Image: Getty)

During the pageantry, the colour was first trooped through the ranks of soldiers before the guardsmen marched past the King, first in slow then in quick time with the King acknowledging the command of “eyes right” with a salute.

In a change from last year, Kate did not join senior family members on a dais, but watched the spectacle from the Duke of Wellington’s former office with her children.

Young Louis got up to his usual cheeky antics, as he was pictured yawning, trying to open a window and dancing to the military music during the impressive display of pomp and pageantry.

At the conclusion of the military spectacle, the members of the Firm travelled back to Buckingham Palace for the iconic balcony appearance.

Stepping out to huge cheers from the thousands gathered outside the steel gates below, the Royal Family put on a united front as they watched the spectacular flypast by the RAF.

The rain briefly relented and blue skies appeared for the show, which concluded with the red arrow display.

The Wales family on the Buckingham Palace balcony (Image: Getty)

Standing shoulder to shoulder, the King’s closeness with his beloved daughter-in-law was for all to see, as Kate was seen leaning over to speak to the King, prompting the pair to giggle and share fond glances at one another.

Garrison Sergeant Major Stokes who helped plan Trooping praised Kate for attending today, he said: “I think it’s such a nice thing for the Princess of Wales to come and attend today.

“It is probably the only day we see the entire royal family together in public and I think the royal family really appreciate the day as well – it’s the closest thing we get in the United Kingdom to a national day, so all of that makes it incredibly special.”

Kate said in a statement on Friday she was making “good progress” with her treatment, but candidly said she has “good days and bad days” and although she has been working from home, said: “I am not out of the woods yet”.

Support from the public has made a deep impression on the princess, who said she had been “blown away” by the “kind messages” that had made a “world of difference to William and me and has helped us both through some of the harder times”.