Following the visit to Windsor, the first lady returns to Washington, D.C. The president travels on to Brussels for two days of meetings with North Atlantic Treaty Organisation and European Commission leaders, and then to Geneva, where he'll conclude his weeklong trip with a summit with Russian President Vladimir Putin.
The 95-year-old monarch first began meeting with US presidents when she was just a 25-year-old princess.
Mr Biden took off his aviator sunglasses before carrying out an inspection of the guard before watching a military march-past. She also asked what life in the White House was like.
"I wish her all the very best".
Biden became the 13th sitting USA president to meet with Queen Elizabeth II during her 69-year reign. "She wanted to know what the two leaders that I. the one I'm about to meet with, Mr Putin, and she wanted to know about Xi Jinping, and we had a long talk".
It generally is frowned upon for anyone to reveal the contents of their private talks with the Queen.
He added: "She said, "What's it like in the White House?' I said, 'Well it's magnificent but it's a lot of people".
They greeted the Queen on a dais in Windsor's quadrangle before a Guard of Honour gave a royal salute as the USA national anthem was played.
He replied: "Yes, we did".
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She sat on a gold chair on the dais in the quadrangle alone as she waited for the official Range Rover carrying the 78-year-old President and First Lady to arrive.
Making one of her few public appearances since the death of her beloved husband Prince Philip, Queen Elizabeth II proved she hasn't lost her humor while rubbing shoulders with world leaders at a G-7 reception on Friday.
She has since met all 14 elected U.S. leaders during her 69 years on the throne, except for Lyndon B Johnson. President Lyndon B Johnson is the only one who did not make her acquaintance while he was in office. "Don't you bow down to her", Biden was told, according to a memoir.
The Bidens were greeted by the Queen's Guard of Honor and then retired to a private tea within the castle.
The traditional Trooping the Colour ceremony, which is normally staged in London, was ruled out for the second successive year because of the threat of coronavirus.
Joe Biden and his wife will become the fourth president and first lady the queen has received at Windsor, following the Trumps in 2018, the Obamas in 2016, President George W. Bush and his wife in 2008 and the Reagans in 1982. It is believed the visit overran by 10 minutes. They also had afternoon tea together in the Oak Room.