The Princess of Wales’ triumphant return to public life was capped by a Buckingham Palace balcony appearance with the royal family in honour of the King’s official birthday.

Kate looked relaxed during her first day in the spotlight following her cancer diagnosis for the traditional Trooping the Colour ceremony, where her youngest child Prince Louis stole the show again.

Louis was pictured yawning, trying to open a window and dancing to the military music as the princess and her young family watched the pomp and pageantry in Horse Guards Parade in honour of the King.

After months of chemotherapy, which is still ongoing, the princess joined what is a family occasion on the national stage but kept a watchful eye on her children.

Her appearance was in doubt after she missed the final Trooping rehearsal last weekend, but with the King also suffering from cancer the spectacle of military pomp and pageantry became a symbolic statement by the monarchy after a period of uncertainty.

During the day 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, a departure from last year because of his illness, and inspected the officers and guardsmen on Horse Guards Parade in Whitehall from the coach rather than from a horse.

Garrison Sergeant Major Stokes who helped plan Trooping praised Kate, 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 and members of the royal family were cheered when they were first spotted in The Mall on their way to Trooping and Carol and Brian Haddow from Scotland were among thousands waiting to catch a glimpse of members of the monarchy.

Mrs Haddow said: “`Well, like anybody going through chemotherapy, it’s a big thing for her to come out and do this. We were a wee bit back but she looked fine, happy to be involved and she was with the kids.”

She said the royal family played an important part in “bringing in tourism” to the country, adding: “It’s a great thing to have a king or queen.”

Kate said in a statement on Friday she was making “good progress” with her treatment but candidly added 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”.

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

During the military spectacle, Louis was seen yawning as he viewed the ceremony from the historic building overlooking the parade ground, and later the young royal danced during the quick march of the Scots Guards to Highland Laddie.

Trooping the Colour is a social as well as a ceremonial occasion and the stands overlooking the parade ground were filled with about 8,000 spouses, girlfriends and parents of the guardsmen and officers on parade.

It featured more than 1,250 soldiers, including hundreds of guardsmen lined up in two rows who were inspected by the King from his carriage with Camilla, Colonel of the Grenadier Guards, followed by the mounted royal Colonels.

The colour, or regimental flag, that was trooped in front of the soldiers, an ancient ceremony to enable servicemen to identify their flag, was the King’s Colour of number 9 company, Irish Guards, the regiment Kate serves as Colonel.

Dark clouds threatened rain but luckily for organisers the downpour came as the royal family left in carriages for their balcony appearance to watch the fly-past, with the rain ending as the first jets roared overhead and the Red Arrows provided the finale.

During the aerial show, William was pictured affectionately pulling Louis’ ears as Kate watched and grinned and when the national anthem was played big sister Charlotte gave her younger sibling a nudge to stand still.

Kate’s appearance was to mark the family occasion and she is not expected to return to full-time royal duties until she has fully recovered.