Joe Biden has praised the Queen’s generosity and said she reminds him of his mother after the monarch hosted him and the First Lady for tea at Windsor Castle.
Biden said he did not think the Queen would "be offended" before he made the remark, as he boarded the Marine One plane at Heathrow to head to Brussels.
The US president and his wife Jill travelled to the Berkshire royal residence on Marine One on Sunday after attending the G7 summit in Cornwall.
Before leaving the UK, Mr Biden, 78, shared details of his conversations with the 95-year-old head of state and revealed he had invited her to visit the White House.
The Bidens landed in the grounds just before 5pm, a few minutes ahead of schedule, and were greeted by the Queen in the castle’s quadrangle.
A Guard of Honour formed of The Queen’s Company First Battalion Grenadier Guards gave a royal salute and the US national anthem was played beneath blue skies and hot sunshine.
Mr Biden accompanied the Officer Commanding the Guard of Honour, Major James Taylor, and Major General Christopher Ghika to inspect the Honour Guard, before returning to the dais to watch the military march-past with the Queen and First Lady.
The Queen was wearing a Stewart Parvin dress in a floral print jacquard in shades of pink, olive and russet, and she teamed it with a hat by Rachel Trevor-Morgan and the diamond Jardine star brooch.
The Bidens walked into the castle with the monarch via the Sovereign’s Entrance at 5.18pm.
Mr Biden walked alongside the Queen who said to the president: “You completed your talks.”
He replied: “Yes we did.”
Before going inside, the Queen introduced the Bidens to her lady-in-waiting Dame Annabel Whitehead.
With bright sunshine overhead, Mr Biden was wearing dark sunglasses when he got out of his vehicle.
The president was wearing a dark suit while Dr Biden was wearing a powder blue skirt suit.
The palace said the couple left at 6.03pm – meaning they spent around 40 minutes inside the castle, with the whole visit lasting more than an hour in total.
It is believed the visit overran by 10 minutes.
The chefs at Windsor Castle have trained in the best restaurants and hotels in the country, and will likely have made classic sandwiches and a range of cakes – with some of the ingredients sourced from royal estates.
The tea in the castle’s Oak Room comes after the Bidens met the Queen on Friday when she attended a reception for G7 leaders at the Eden Project.
Following the visit and before his departure from the UK, Mr Biden spoke about the Queen to reporters.
He said they had spoken about Russian president Vladimir Putin and China’s leader Xi Jinping.
Mr Biden said: “We had a long talk. She was very generous. I don’t think she’d be insulted but she reminded me of my mother.
“In terms of the look of her and just the generosity. She was very gracious.”
He added he had invited the monarch to the White House, saying: “She said, ‘What’s it like in the White House?’ I said, ‘Well it’s magnificent but it’s a lot of people’.”
The carefully-choreographed arrangements to welcome Mr Biden echo the welcome given to Donald Trump in 2018, when the controversial then-US president travelled to Windsor to meet the monarch.
On that occasion however, the Queen joined Mr Trump in inspecting the troops.
As they walked across the lawn to view the troops, the Queen appeared to gesture and point several times for him to move closer to the front line of soldiers.
Mr Trump moved slightly nearer but then stood still in front of the Queen, meaning she had to navigate her way around him so they could walk side by side.
Escorting a visiting head of state to inspect the troops is a role which usually fell to the late Duke of Edinburgh, before he retired in 2017.
Mr Trump and the Queen had afternoon tea together, also in the Oak Room, with the meeting lasting longer than expected.
It was due to last around half-an-hour, but overran by almost 20 minutes.
The Queen also entertained the Obamas at Windsor Castle in 2016 when the Duke of Edinburgh, then 94, famously drove Mr and Mrs Obama the short distance to the castle after Marine One touched down on the lawns of the residence.
In 2008, when then-US president George W Bush met with the monarch at Windsor, he enjoyed a traditional English afternoon spread of tea, small sandwiches and cakes in the White Drawing Room.
There have been 14 US presidents during the Queen’s 69-year reign – from Harry S Truman to Mr Biden.
Mr Biden, who is in the UK for the G7 summit, will be the 13th American leader to meet the monarch, with Lyndon B Johnson the only one the Queen has not met.
Her tea with Mr Biden comes the day after the Queen received her official birthday gift from the nation’s armed forces – a ceremony of pomp and pageantry in her honour – which was held at 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.