President Donald Trump and First Lady Melania Trump arrived at Buckingham Palace on Tuesday for a NATO anniversary reception.

The event was held to celebrate 70 years of collaboration in the NATO alliance.

Among the royal attendees was hostess Queen Elizabeth herself, who was seen greeting the first family at the door, as well as Prince Charles and his wife Camilla, Duchess of Cornwall.

Queen Elizabeth II, Prince Charles and Duchess Camilla welcome Donald and Melania Trump to Buckingham Palace. Her Majesty Queen Elizabeth II hosted the reception for NATO Leaders to mark 70 years of the NATO Alliance. (Photo by Geoff Pugh - WPA Pool/Getty Images)

Queen Elizabeth II, Prince Charles and Duchess Camilla welcome Donald and Melania Trump to Buckingham Palace. Her Majesty Queen Elizabeth II hosted the reception for NATO Leaders to mark 70 years of the NATO Alliance. (Photo by Geoff Pugh - WPA Pool/Getty Images)

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Also in attendance was Kate Middleton, Duchess of Cambridge and wife of Prince WilliamPrincess Anne was also at the reception.

Catherine, Duchess of Cambridge attends a reception for NATO leaders hosted by Queen Elizabeth II at Buckingham Palace on December 3, 2019 in London. (Photo by Yui Mok - WPA Pool/Getty Images)

Catherine, Duchess of Cambridge attends a reception for NATO leaders hosted by Queen Elizabeth II at Buckingham Palace on December 3, 2019 in London. (Photo by Yui Mok - WPA Pool/Getty Images)

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Ahead of Tuesday's reception, Trump, 73, and Melania, 49, had tea with Charles and Camilla at Clarence House, which is the second time that the president and the first lady have attended such an event.

Meanwhile, following the reception, Anne and her brother Edward later hosted the Trumps in the state rooms of the palace, according to USA Today.

Princess Anne attends a reception at Buckingham Palace on Tuesday, Dec. 3, 2019. (Yui Mok/Pool Photo via AP)

Princess Anne attends a reception at Buckingham Palace on Tuesday, Dec. 3, 2019. (Yui Mok/Pool Photo via AP)

Absent from the reception were William, who is currently on an official visit to Kuwait and Oman, along with Prince Harry and his wife Meghan Markle, as they are taking a break from royal duties until the new year.

Prince Charles and Duchess Camilla of meet with Donald Trump and wife Melania at Clarence House on December 3, 2019 in London. (Photo by Victoria Jones - WPA Pool/Getty Images)

Prince Charles and Duchess Camilla of meet with Donald Trump and wife Melania at Clarence House on December 3, 2019 in London. (Photo by Victoria Jones - WPA Pool/Getty Images)

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According to People magazine, the Trumps are expected to attend another reception hosted by U.K. Prime Minister Boris Johnson on Tuesday. They are set to return to the U.S. by Thursday.