US president Barack Obama and the First Lady have given the Queen a 90th birthday present - a reminder of her many visits to America.
The Queen was presented with a photo album chronicling her official engagements with US leaders and their wives.
Over the past decades Britain's head of state has made numerous trips across the Atlantic, from her first in 1951, when Princess Elizabeth, which saw her tour George Washington's historic Mount Vernon estate and meet President Harry S Truman.
She also visited Ground Zero in New York in 2010, the site of the 9/11 terrorist attacks, where she paid her respects.
The Queen is the nation's longest serving monarch who celebrated her 90th birthday on Thursday with a walkabout in Windsor and a black tie dinner with her family.
She was given armfuls of presents by members of the public, from cards and dozens of bouquets of flowers to a cake made by The Great British Bake Off winner Nadiya Hussain.
The Obamas have a warm relationship with the Queen and her family and were invited to have lunch with the monarch and the Duke of Edinburgh at Windsor Castle, ahead of talks the president held with the Prime Minister.
In an ITV documentary to mark the Queen's 90th birthday, Mr Obama praised the Queen for her "generous human touch'' as he credited the monarch with helping to ensure the lasting special relationship between the UK and America.
In 2009, after a photocall for G20 leaders at Buckingham Palace, the Queen and Michelle Obama were seen putting their arms around each other's backs.
A Buckingham Palace spokeswoman described it at the time as a "mutual and spontaneous display of affection and appreciation" between the two women.
They formed a strong friendship, bonding over a shared interest in the countryside, gardening and clothes.
As they said goodbye at the end of the visit in 2009, the Queen was overheard asking Mrs Obama: "Now we have met, would you please keep in touch?"
A successful state visit to the UK followed in 2011, and Mrs Obama has also returned to London privately with her daughters, Sasha and Malia, when they were given a guided tour of Buckingham Palace by palace staff.
Prince Harry has a close friendship with Mrs Obama in particular - through his support of wounded military personnel and his work with the Invictus Games, a Paralympic-style championship for injured military personnel from across the globe. Mrs Obama is a keen supporter of forces' families in the US.
The monarch is well used to hosting American leaders - Mr Obama is the 12th US president of her reign and the Queen has met all of them, except one - Lyndon B Johnson.
Philip showed the US leader and his wife the personal touch when he drove them and the Queen to Windsor Castle after the Marine One presidential helicopter had landed close to the monarch's Berkshire home.
The gesture was akin to picking up guests from the airport although the journey only lasted a few minutes, but Mr Obama looked delighted when he discovered Philip would be driving them.
The Queen, who wore a powder blue jacket and matching skirt, and Mrs Obama, reportedly dressed in a Oscar de la Renta print dress and Narciso Rodriguez coat, sat on the rear seats.
The Duke may be approaching his 95th birthday in June but he looked composed at the wheel of the Range Rover as it made its way around the castle's quadrangle and stopped outside the sovereign's entrance.
Inside the foursome posed for a photograph in the castle's Oak Room, in the Queen's private apartment.
The monarch uses the room to hold audiences and in past years has recorded her Christmas broadcast there.
The private lunch lasted around an hour before the Queen and Philip said goodbye to the outgoing US leader and his wife.
Later the Obamas will be the dinner guests of the Duke and Duchess of Cambridge and Harry at Kensington Palace.