Kate Middleton picture: Princess of Wales releases new photo and plans to join royal family at Trooping the Colour

Despite the challenges, she has begun working from home, participating in meetings with her foundation and Kensington Palace team. She said she hopes to "join a few public engagements over the summer" but stressed she is "not out of the woods yet."

Since late February, the princess has been receiving treatment for an undisclosed type of cancer. Her decision to appear at a significant national event this Saturday has been positively received by the King. A recent photo taken at Windsor Castle shows Kate in a smart casual outfit, standing in a peaceful setting by a weeping willow tree near water.

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.”

She also saod: “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.”

The princess will be accompanied by her three children, Prince George, Princess Charlotte, and Prince Louis, in a carriage for the Trooping the Colour procession. They will later join other royals on Buckingham Palace’s balcony for the fly-past.

Kate added: “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. I am learning how to be patient, especially with uncertainty. Taking each day as it comes, listening to my body, and allowing myself to take this much needed time to heal.”

The future Queen has been touched by the outpouring of support, receiving thousands of letters and cards from well-wishers, some sharing their own cancer battles. She said “kind messages” had made a “world of difference to William and me and has helped us both through some of the harder times.”

A Buckingham 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.”