Kate, Princess of Wales, has waved to crowds and smiled broadly from the balcony of Buckingham Palace after watching a military parade, making her first public appearance this year as she undergoes treatment for cancer.
The princess, 42, spent two weeks in hospital in January after she underwent major abdominal surgery.
Two months later she announced in a video message that tests had revealed the presence of cancer and she was receiving preventative chemotherapy.
She is still undergoing treatment but her improved health meant she was able to appear in public for the first time since December.
The princess rode in a covered carriage with her three children to watch the "Trooping the Colour," an annual military parade to mark the official birthday of King Charles.
Despite heavy rain showers, crowds lined the streets and 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 by fashion designer Jenny Packham and a broad-brimmed matching hat by milliner Philip Treacy, 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 while Charles saluted passing troops from a covered dais on the parade ground itself.
The King and Queen, as well as William, Kate and other members of the royal family later returned to Buckingham Palace to watch a military fly-past from the balcony.
Kate smiled broadly and waved.
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'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.
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.
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 daily commitments are being limited to minimise risks to his recovery.
