Kate Middleton makes her public return at a military parade honoring King Charles III

Britain is putting on a display of birthday pageantry Saturday for King Charles III, a military parade that marked the Princess of Wales’ first public appearance since her cancer diagnosis early this year.

The annual event is also a show of stability by the monarchy after months in which both the king and Kate, wife of heir to the throne Prince William, have been sidelined by cancer treatment.

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Kate announced Friday that she would attend the King’s Birthday Parade after making progress in her treatment. She disclosed in March that she was undergoing chemotherapy for an unspecified form of cancer.

“I am making good progress, but as anyone going through chemotherapy will know, there are good days and bad days,” Kate said in a statement, adding that she faces “a few more months” of treatment.

The 42-year-old princess was seen smiling in a horse-drawn carriage with her three children as the procession made its way from Buckingham Palace to Horse Guards Parade. Prince Louis, 6, was captured waving to the crowds from the carriage window.

Kate joined other members of the royal family on a Buckingham Palace balcony at the end of the King’s Birthday Parade. The 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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Prince William was on horseback for the ceremony, also known as Trooping the Color, in which troops in full dress uniform parade past the king with their regimental flag, or “color.” Charles, who also is being treated for an undisclosed form of cancer, carried out the ceremonial review of the guardsmen and officers from his carriage.

Charles, 75, disclosed his cancer in February, and has recently eased back into public duties. He attended commemorations last week for the 80th anniversary of D-Day, the Allied invasion of Nazi-occupied Europe on June 6, 1944.

Kate said in her statement on Friday that she is “not out of the woods yet” and officials stress that Saturday’s engagement does not herald a full return to public life.

In one of the many quirks of British royal convention, Saturday is not the king’s real birthday -– that’s in November. Like his mother Queen Elizabeth II before him, Charles has an official birthday on the second Saturday in June. The date was chosen because the weather is generally good, though early sunshine on Saturday gave way to a blustery, rainy day in London.

Royal fans in raincoats and umbrellas had already gathered along the route several hours before start time, along with a smattering of anti-monarchist protesters chanting “Not my king.”

Spectators were treated to a display of pomp and precision involving more than 1,000 soldiers, 250 military musicians and more than 200 horses. The equine participants included Trojan, Tennyson, and Vanquish, three of the five military horses who sparked mayhem in April when they bolted and ran loose through central London.

The horses were performing routine exercises near Buckingham Palace on April 24 when they became spooked by noise from a nearby building site and galloped loose through the capital’s streets, crashing into vehicles and causing chaos during the morning rush hour.

The army says the other two horses are recovering well and are expected to return to duty.

Where can I watch Trooping the Colour?

You can watch live coverage of the parade starting at 5:30 a.m. ET, 10:30 a.m. local time on Sky News and on BBC.

In what events will Kate take part in Trooping the Colour?

As in previous years, Kate will join the royal family on a Buckingham Palace balcony to watch the military flyover.