US president Barack Obama renewed friendships with the Queen and strengthened ties with Britain today on his first state visit to the UK.
The American leader and his wife Michelle were given a warm welcome by the monarch and the Duke of Edinburgh, met newlyweds the Duke and Duchess of Cambridge and headed to Downing Street at the start of their three-day stay.
The state visit comes at a time of close co-operation between Britain and the US on Libya, Afghanistan, counter-terrorism and the Middle East peace process.
At Westminster Abbey, following a wreath-laying at the Grave of the Unknown Warrior, the First Lady Mrs Obama was heard to remark: "It's so nice to be back."
Following a courtesy call on the Prime Minister and his wife Samantha, Mr Obama and Mr Cameron dropped in on a south London school. The two leaders took off their jackets and teamed up to play table tennis against two teenage schoolboys.
But the Anglo-American team took a sound beating at the hands of 16 year olds Jason Do and Jamiyu Mojaji at the Globe Academy in Southwark.
"Who wants to take me on?" Mr Obama said as he walked into the gym, before adding: "You can't have the old guys against the young."
Earlier, during a windy welcome ceremony on the terrace of Buckingham Palace, Mrs Obama was left desperately protecting her modesty. Strong gusts had the First Lady clutching her dress as it threatened to blow up into the air during the event in the palace gardens.
The wind also caused havoc with Mrs Obama's hair which was standing on end at one point, while the Queen and Duchess of Cornwall had to hang on to their hats.
On the garden lawn were the Guard of Honour, 101 soldiers from the 1st Battalion, Scots Guards, and three officers lined up in two rows. Behind them were the band, pipes and drums of the Scots Guard. The guardsmen gave a royal salute and then the US national anthem was played in honour of the president.
At the grand entrance the US leader exchanged words with the Queen as he gave her a double handshake and greeted Philip, telling him: "Nice to see you sir."
The Queen and the Duke took the Obamas on a tour of the picture gallery, where an exhibition of US memorabilia was put on display by the Royal Collection.
When President Obama was shown letters and artefacts charting Britain's loss of the American colonies, he joked: "That was only a temporary blip in the relationship."
A motorcade of 19 cars and coaches, including a London ambulance, escorted the president in his armoured cadillac, known as The Beast, around the capital.
William and Kate had travelled to the palace especially to see them. Kate was pictured deep in conversation with Mrs Obama, on what was her first royal duty as a member of the royal family, while William talked with the president.
They spent around 20 minutes with the couple in the Palace's grand 1844 room.
The Obamas did not attend the recent royal wedding, with this state visit seen as a sweetener instead. They are staying as guests of the Queen and will occupy the palace's Belgian suite, as is customary for visiting foreign heads of state. It was there that William and Kate spent their first night as a married couple following their wedding.
Tonight Mr and Mrs Obama will be wined and dined at a state banquet for 170 guests in the palace ballroom.
A joint article written for The Times newspaper by Mr Obama and Mr Cameron said today: "Ours is not just a special relationship, it is an essential relationship - for us and for the world."
Tomorrow will be devoted to politics, with talks between the leaders at Downing Street, followed by an address to both Houses of Parliament, in which the president is expected to say that the US has no closer ally in the world than Britain.
The two leaders are also expected to drop in on a barbecue being hosted by their wives for families of military personnel involved in joint UK-US missions overseas.