Prince George met Barack Obama in his pyjamas as his mother and father hosted the US president and the first lady at Kensington Palace.
The two-year-old, wrapped up in check pyjamas and a white dressing gown, was allowed to stay up late and managed to show the couple his rocking horse and the stuffed toy they had given him when Princess Charlotte was born before bedtime.
It capped the end of a long day for Mr Obama and his wife Michelle, who earlier on Friday had lunched with the Queen and the Duke of Edinburgh.
Mr Obama paid a glowing tribute to the Queen just a day after her 90th birthday, describing her as an 'astonishing person and a real jewel'.
As the Obamas arrived, to be greeted by the Duke and Duchess of Cambridge and Prince Harry in the courtyard of 1A Kensington Palace, the president shouted 'oh there you are - hello'.
The pair sheltered from the rain under a single black umbrella after they stepped out of the presidential black Cadillac.
William, wearing a blue jacket, blue trousers and white shirt without a tie, apologised to the Obamas, saying: 'Sorry about the weather'.
Kate, wearing a teal and maroon dress, shook hands with the president and his wife, who was wearing a long camel coat over a lighter camel dress, before Mr Obama offered her the umbrella.
But the Duchess refused it, leaving the US leader to hold it over both his wife and Kate.
The five chatted briefly, laughing together several times, before moving to pose for photos without the umbrella.
As they chatted in the courtyard, William was heard to say: 'You've had a long day?'
To which Mr Obama, wearing a black suit and open-necked white shirt, replied: 'We've enjoyed it.'
As they went inside for dinner, they found an eager Prince George awaiting them.
A Kensington Palace spokesman said: 'Prince George stayed up to meet the president and first lady when they arrived at Kensington Palace.
'He was able to show the president and first lady a rocking horse - given to George when he was born - and a stuffed toy - given to George when Princess Charlotte was born - that had been previously given to him by president and Mrs Obama.'
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