The reunion at Highgrove House is the family's first known meeting since 2022.
William and Kate were married on April 29, 2011, at Westminster Abbey.
King Charles III acknowledged "times of great uncertainty" as he expressed gratitude to the American people and marked the 250th anniversary of independence from Britain in a speech to the U.S. Congress that highlighted the bonds between the two countries at a time of political turmoil.
Britain's royal family is leading commemorations for what would be the 100th birthday of the late Queen Elizabeth II.
King Charles III and his wife Queen Camilla are coming to America for their first official state visit to the country.
The appearance marks the couple's first joint attendance at the awards show in three years.