Kate, Britain's Princess of Wales, made her first public appearance on Saturday since surgery five months ago revealed the presence of cancer, attending a military parade in central London.

Kate rode in a covered carriage with her three children before watching the "Trooping the Colour", an annual military parade near Buckingham Palace that marks the official birthday of the British monarch, King Charles.

Crowds lining the streets waved and cheered as the carriage went past, outnumbering a small group of protesters holding placards calling for an end to the monarchy.

Charles rode in a separate carriage with Queen Camilla, followed by Prince William, Charles' heir and Kate's husband, who was on horseback along with other senior members of the royal family.

Kate, wearing a pale outfit decorated with a white and navy ribbon and a broad-brimmed matching hat, watched the ceremony from a window overlooking the parade ground. She pointed out aspects of the event to her children Prince George, Princess Charlotte and Prince Louis.

Charles saluted passing troops from a covered dais on the parade ground itself.

Back in the carriage at the end of the parade, the princess smiled and waved at the crowds, who by this point were being drenched in driving rain.

Kate, 42, has undergone preventative chemotherapy since the cancer announcement, and while treatment is continuing, her improved health meant she was able to appear in public for the first time since last December.

In a rare personal written message on Friday, she said she was making good progress but was "not out of the woods". She said she was looking forward to attending Saturday's parade and hoped to join a few public engagements over the summer.

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.

'FABULOUS'

Before the parade, onlookers said they were looking forward to seeing the princess.

"I know it's the king's birthday, but all eyes will be on Kate because we haven't seen her for a while," said John Loughrey, who was wearing a T-shirt with pictures of Kate on it.

Another onlooker, Anne Gaely, who was carrying a life-size cardboard cutout of the princess, said she was relieved that Kate would be there in the flesh.

"We've all been very, very worried and uneasy about it, but now this is going to be joyful, euphoric, and fabulous," she said.

In her message on Friday, Kate said she had been "blown away" by thousands of kind messages from across the globe, which had made a world of difference to her and William.

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

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

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.