Kate Middleton, the Princess of Wales, who is currently undergoing chemotherapy for cancer treatment, said she will attend King Charles III's birthday parade on the weekend, marking her first public appearance in six months.

The 42-year-old future queen said in a statement she was "making good progress" with her chemotherapy treatment for unspecified cancer, and that it would continue "for a few more months."

Kate said she hoped to join in "a few public engagements over the summer" months as well as Saturday's annual Trooping the Colour parade for Charles's official birthday.

The statement was released on Kate's social media channels alongside a photograph -- taken earlier this week in Windsor, west of London -- of the princess standing in front of a tree next to a river.

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

Kate, married to heir-to-the-throne Prince William and mother to their three young children, noted that she has started to do "a little work from home" on days when she "feels well enough".

"It is a joy to engage with school life, spend personal time on the things that give me energy and positivity," she 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," Kate said.

"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."

Kate, who was last seen at a public engagement when the royals gathered for Christmas last December, revealed in March that she had been diagnosed with cancer.

It followed Charles in February announcing that he had been diagnosed with an unspecified form of cancer.

The king, 75, has also been receiving treatment and in April royal officials said doctors were "very encouraged" by his progress, allowing him to resume his official duties.

However, he will participate in this year's birthday parade from a carriage, rather than on horseback as he did last year.