Royals Prince George in His Pajamas Shaking Hands with President Obama Is the Greatest Moment in U.S.-British History "The three of them have built up a relationship with the President and First Lady over the years," a palace source tells PEOPLE By Simon Perry Published on April 22, 2016 03:00 PM Share Tweet Pin Email Photo: Kensington Palace Prince George made a surprise appearance at Kensington Palace on Friday – in his pajamas! The little royal, who stole the spotlight earlier in the week in his cutest royal portrait yet, appeared in a hallway wearing a plush robe (embroidered with his name!), matching gingham blue pajamas and slippers just before the start of his parents’ dinner with President Barack Obama and First Lady Michelle Obama. In a photo shared on Kensington Palace’s Twitter, George can be seen sharing a handshake with the President. Other pictures show him riding a rocking horse – a gift from the Obamas when he was born. Although George, who turns 3 in July, was permitted to stay up late for the special occasion, his nearly 1-year-old sister Princess Charlotte was fast asleep, says a palace source: “George stayed up for a few minutes when the President and the First Lady arrived, but Charlotte was in bed.” (George had previously been playing with a plush version of First Dog Bo, a past gift from the Obamas.) Prince William, Princess Kate (in an L.K. Bennett dress) and Prince Harry are hosting the First Couple for a private dinner, with Harry warmly greeting Mrs. Obama with a double kiss. The special evening – which followed lunch Buckingham Palace with the Queen – was arranged by William on behalf of all three royals, and “they were delighted that [the First Couple] were able to accept,” a palace source tells PEOPLE. “The three of them have built up a relationship with the President and First Lady over the years,” adds the source. Kate, who wore a teal and purple LK Bennett dress, and William first met the couple at Buckingham Palace in 2011 just after the royal wedding. It was their first joint engagement as a married couple. In 2014 William visited the Oval Office, where he and President Obama discussed the campaign to clamp down on illegal wildlife trafficking. Of course, Prince Harry has his own special relationship with the White House – and in particular with Mrs. Obama. Last June, he hosted the First Lady and First Daughters Malia and Sasha – along with grandma Marian Robinson – for tea at Kensington Palace. • Want to keep up with the latest royals coverage? Click here to subscribe to the Royals Newsletter. Then in October, it was the First Couple’s turn to play host to a visiting Prince Harry – where the chemistry between Mrs. Obama and the royal was on adorable display. The two will be reunited once again next month, when they team up in Orlando for Harry’s Invictus Games for veterans.