Barack Obama met with Princess Elisabeth just 24 hours before holding undisclosed private talks with Prime Minister Rishi Sunak.
The princess took time out of her studies in Oxford to greet the former US president in Brussels.
The future Queen of Belgium and her father King Philippe met Obama at the Castle of Laeken in Brussels on Sunday.
The last time Barack Obama was welcomed by King Philippe to the palace was in 2014 as part of a state visit.
The future Queen of Belgium met with former US president Obama
Instagram/ @belgianroyalpalace
Later in the day, Obama travelled to Antwerp to give a speech at a technology conference.
The visit to Belgium came before Obama arrived at Downing Street on Monday for a surprise meeting with Rishi Sunak.
This was the first time Obama had met Sunak.
A Downing Street spokesperson insisted the visit was an “informal courtesy drop in” while Obama was in London.
They added: "President Obama’s team made contact and obviously the prime minister was very happy to meet with him and discuss the work of the Obama Foundation."
Princess Elisabeth, 22, welcomed the special guest of honour in her home country wearing a striking blue suit.
In a picture posted by the Belgian Royal Palace, the princess wore a belted blue suit jacket with matching trousers next to the former president and her father.
Royal fans praised the princess for her outfit and her professionalism on social media.
Princess Elisabeth currently studies at Lincoln College in Oxford, England
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One fan wrote: “The Crown Princess is looking so awesome in blue,” and another said: “Such a beautiful blue outfit for the princess.”
The princess currently studies history and politics at Lincoln College in Oxford, England.
Before studying at Oxford, the princess obtained her International Baccalaureate at UWC Atlantic College in Wales.
Elisabeth, the eldest child of King Philippe and Queen Mathilde, will be Belgium’s first female monarch when she becomes Queen.
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Princess Elisabeth is the eldest child of King Philippe and Queen Mathilde
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Royal fans were happy to see the princess carrying out royal engagements while continuing her education.
One person said: “The King can be proud of his daughter” and “Wow for Princess Elisabeth.”
Elisabeth, who is titled the Duchess of Brabant, has three younger siblings, Prince Gabriel, 20, Prince Emmanuel, 18 and Princess Eleonore, 15.
She is also multilingual and can fluently speak Dutch, French, German and English.