The NATO summit officially kicked off in London and Queen Elizabeth II hosted a grand reception with the world leaders, including U.S. President Donald Trump.
First Lady Melania Trump, who wore a yellow Valentino coat, was also in attendance with her husband, where they reunited with with Prince Charles and Camilla at Buckingham Palace.
Earlier that day, the Trumps had tea with the royal couple at Clarence House.
Other world leaders in attendance at the reception included Chancellor of Germany Angela Merkel and Prime Minister of Canada, Justin Trudeau.
Kate Middleton attended the gathering solo, as Prince William is currently on a royal visit to Kuwait and Oman.
The Duchess of Cambridge stunned in a green Emilia Wickstead dress as she mingled with leaders from around the world at the palace.
The Queen was also glamorous in green, accessorizing her look with an emerald green shawl and pearl jewelry.
Tuesday’s reception at Buckingham Palace is just one of the main events of the two-day NATO meeting, with this occasion celebrating the 70th birthday of the alliance.