Kate Middleton joined by kids George, Louis and Charlotte at Trooping the Colour

Prince George, Princess Charlotte and Prince Louis joined their parents Prince William and Kate Saturday for an annual royal event.

The Wales siblings joined their parents at Trooping the Colour, the annual military parade marking the official birthday of their grandfather, King Charles III.

During the parade, George, 10, Charlotte, 9, and Louis, 6, rode with their mom in a state carriage down the Mall.

The siblings were seen looking out the windows of the carriage and waving to crowds gathered to take part in this year's festivities.

After they finished their carriage ride, George, Charlotte and Louis were seen alongside Kate watching the rest of the parade from a window at Buckingham Palace.

The siblings then joined William and Kate and other senior members of the royal family on the balcony of Buckingham Palace, where they watched the military flyover.

Trooping the Colour marked the first public appearance for Kate, 42, since December, when she and William and their children attended a Christmas Day service in Sandringham.

Shortly after that appearance, Kate was hospitalized in mid-January for what Kensington Palace described as a "planned abdominal surgery."

After taking time off from public duties to recover, Kate shared in a recorded video message in March that she had been diagnosed with cancer. She said at the time that the cancer had been discovered in post-operative tests after her abdominal surgery.

The type of cancer has not been disclosed. According to Kensington Palace, Kate started a course of preventative chemotherapy in late February.

In announcing her diagnosis, Kate described how it had impacted her family, saying, "This of course came as a huge shock, and William and I have been doing everything we can to process and manage this privately for the sake of our young family."

On Friday, Kate shared her first update on her health since announcing her diagnosis.

"I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days," Kate said in a written message shared by Kensington Palace. "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 said her treatment will continue "for a few more months," adding, "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."