Charles and Queen Camilla were joined by members of the royal family, including Prince William and Kate, the Princess of Wales and their three children, in the annual military parade, held to mark the reigning monarch's official birthday.
While Charles and William, the heir to the throne, rode in the parade on horseback, Camilla, Kate and her kids, Princes George and Louis and Princess Charlotte, rode together in an open carriage.
Kate, dressed in green, sat alongside Camilla, across from George, Louis and Charlotte.
George, 9, and Louis, 5, wore dark suits for the occasion, while Charlotte wore a red and white dress with her hair styled off her face in braids.
In addition to members of the royal family, over 1,400 parading soldiers, 200 horses and 400 musicians are participating in the military parade, described by Buckingham Palace as "a great display of military precision, horsemanship and fanfare."
Also part of Saturday's festivities is a military flypast over Buckingham Palace, which the royal family watches from the palace's balcony.
Louis' animated facial expressions during the flypast and parade stole the show.
The military flypast includes 70 aircraft, according to the palace.
This year's Trooping the Colour is the first major public event together for the royal family since Charles' and Camilla's coronation, held last month at Westminster Abbey.
Absent from Saturday's festivities are Charles's younger son, Prince Harry, who traveled from California, where he now lives with his family, in May to attend the coronation.
A spokesperson for Harry and his wife, Meghan, the Duchess of Sussex, confirmed to ABC News that the couple would not be coming to Charles’ first Trooping the Colour as king. They were not invited because they are no longer senior working royals, having stepped down from those roles in 2020.
Last year, the Trooping the Colour took place amid the Platinum Jubilee celebrations for Charles's mother, Queen Elizabeth II, who passed away three months later, in September 2022.