United States President Joe Biden flew to Brussels for the 31st summit of the North Atlantic Treaty Organization Monday after a visit with Queen Elizabeth II while in town for the Group of Seven Summit.

Biden became the 13th U.S. president to meet the British Queen.

"She was very gracious," Biden said before he boarded Air Force One for Brussels. "She reminded me of my mother," he said.

Biden arrived Sunday at Windsor Castle on board the presidential helicopter and was ferried to the Queen in a black Range Rover.

The Queen, wearing a bright pink floral outfit, greeted Biden and his wife Jill in the quadrangle of the castle - home to the royal family for almost 1,000 years. The couple were treated to a taste of British pomp, The Independent reported.

On Twitter, Jill Biden thanked the Queen for her graciousness.

Soldiers from the Queen's 1st Battalion Grenadier Guards gave a royal salute and the Bidens placed their hands over their hearts during the U.S. national anthem.

During their meeting, the Queen and Biden discussed world leaders Xi Jinping and Vladimir Putin, as well as life in the White House compared with Windsor.

Biden's visit was among the 95-year old monarch's first public engagements since the death of her husband Prince Philip in April.

Asked what life in the White House was like, Biden told the Queen "we could fit the White House in the courtyard" of Windsor Castle.

The president extended an invitation for the Queen to visit the White House.

The Queen has welcomed four other U.S. presidents to Windsor - Donald Trump in 2018, Barack Obama in 2016, George W. Bush in 2008 and Ronald Reagan in 1982, The Associated Press said.