Royal fans arrive to support Kate ahead of Princess of Wales's first appearance this year

Kate, who has been receiving treatment for an undisclosed form of cancer, will ride in a carriage alongside her three children, Prince George, Princess Charlotte and Prince Louis, for the traditional procession through London today.

At 1pm, she is expected to gather with King Charles and Queen Camilla, her husband Prince William and other royals on the Buckingham Palace balcony for the RAF flypast.

Scotland Yard has a "substantial" policing operation for the event, with anti-monarchy group Republic being 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."

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 the Horse Guards Parade from 9am, with the parade starting at 10am.

On Friday, Kate issued a written message, saying she experiences "good days and bad days" during chemotherapy.

The Princess of Wales added that she has begun to work from home, undertaking meetings with her foundation and the Kensington Palace team, and hopes "to join a few public engagements over the summer".

However, she stressed: "I am not out of the woods yet."

The princess's decision to choose a major national event to return briefly to the public spotlight has been welcomed by King Charles.

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A new photograph of the royal, taken earlier this week on the grounds of the Windsor Estate, shows Kate in a Blaze Milano blazer underneath a willow tree.

In her statement, Kate said: "I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days. On those bad days you feel weak, tired and you have to give in to your body resting.

"But on the good days, when you feel stronger, you want to make the most of feeling well.

"My treatment is ongoing and will be for a few more months. On the days I feel well enough, it is a joy to engage with school life, spend personal time on the things that give me energy and positivity, as well as starting to do a little work from home."