Watch: Kate, Princess of Wales, attends King Charles' Trooping the Color parade

LONDON - Kate Middleton watched King Charles III’s Birthday Parade from a Buckingham Palace balcony Saturday, joining the royal family for her first public appearance since her cancer diagnosis early this year.

The appearance was expected after the Princess of Wales announced Friday she would be attending the event. In a post on X (formerly Twitter), Kate said she is "making good progress" with chemotherapy treatment.

The 42-year-old princess traveled in horse-drawn carriage from Buckingham Palace down the grand avenue known as the Mall with her children George, 10, Charlotte, 9, and 6-year-old Louis. Bystanders cheered as they caught a glimpse of Kate, dressed in a white dress by designer Jenny Packham and wide-brimmed Philip Treacy hat.

The royal family and crowds outside the palace watched a flyby of military aircraft to cap ceremonies marking the monarch’s official birthday.

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"I have been blown away by all the kind messages of support and encouragement over the last couple of months. It really has made the world of difference to William and me and has helped us both through some of the harder times," she said on X Friday. 

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

Huge crowds turn out each June to watch the king’s birthday parade, also known as Trooping the Color, which begins with a procession involving horses, musicians and hundreds of soldiers in ceremonial uniform from Buckingham Palace. 

Charles was also diagnosed with cancer earlier this year, but has since returned to public duties. 

Kate said Friday that she hopes to make a few more public appearances 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," Kate said on X Friday. 

The Associated Press contributed to this report.