In a personal written message released on Friday, Kate said she had been "blown away" by the thousands of kind messages from across the globe that followed her cancer announcement in March.

She said they had made a world of difference to her and her husband, heir-to-the-throne Prince William.

"I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days," her statement said.

"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."

Her improved health means she will be able to appear in public for the first time since last December, when she joined other senior royals for an annual Christmas Day church service.

On Saturday morning, Kate, 42, will accompany her three children, Princes George and Louis and Princess Charlotte, in a carriage during "Trooping the Colour", an annual military parade held in central London to mark the monarch's official birthday.

She will also join King Charles, Queen Camilla and the other senior family members on the balcony of Buckingham Palace, the high-profile pinnacle of the event.

While Kate said she was hoping to take part in other events this year, aides cautioned that Saturday did not mark a return to a full schedule of work.

"My treatment is ongoing and will be for a few more months," she said. "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."

ABDOMINAL SURGERY

Kate spent two weeks in hospital in January after she underwent major abdominal surgery, and two months later she announced in a video message that tests had revealed the presence of cancer, and she would begin preventative chemotherapy.

Her office, Kensington Palace, has declined to give further details about the type of cancer or about her treatment, other than to say the preventative chemotherapy had begun in February.

In her message, Kate said on days when she felt well it was "a joy to engage with school life, spend personal time on the things that give me energy and positivity". As part of that, she was starting to do work from home, and was able to hold some meetings.

"I am learning how to be patient, especially with uncertainty," said the princess, who is often known by her maiden name Kate Middleton. "Taking each day as it comes, listening to my body, and allowing myself to take this much needed time to heal."

A new photo of the princess was also released to coincide with her message, showing Kate looking well dressed in a jacket and jeans, standing under a tree on the Windsor estate to the west of London, where the family home is located.

Her illness has coincided with that of Charles, 75, who has also been undergoing treatment for cancer. He returned to public duties in April, and has remained busy, although his diary commitments are being limited to minimise risks to his recovery.

"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," a Buckingham Palace spokesperson said.

Prime Minister Rishi Sunak said the whole country would be behind Kate, adding her statement was brave, honest and "wonderful news".

"I'm sure it will bring an enormous amount of comfort to so many other people who are grappling with similar health challenges," he said at a press conference at a G7 conference in southern Italy.

"I think she deserves enormous praise for what she said and it'll be great to see her there tomorrow."

Kensington Palace also said William was pleased to see Kate starting to return to the work and projects that were so important to her.

"He will continue to focus his time on supporting his wife and children, while continuing to undertake his public duties," a spokesperson said.