The Belgian royals touched down in the capital shortly before noon for a flying one-day trip, after being slightly delayed by fog over London.
Mathilde was beautiful in a monochrome ensemble with matching black and white heels, a black clutch bag, headpiece and pearl earrings for her lunch with the Queen.
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Philippe somewhat matched his wife in a smart black suit and tie, with a white handkerchief peeping out from his suit jacket pocket.
Britain’s monarch, 87, wore a cream dress, black shoes and bag, along with her trademark three-string pearl necklace, to welcome the couple.
The royals enjoyed a private lunch at Buckingham Palace, where there were joined by the Duke and Duchess of Gloucester and the Duke of Kent. Other royal attendees were the Queen's famous corgis, who were also there to greet her guests.
Following lunch at the Palace, the Belgian monarch and his stylish wife headed to Westminster Abbey where King Philippe laid a wreath at the Tomb of the Unknown Soldier. The couple were given a tour of the Abbey and made sure they signed the guestbook before leaving.
A reception at the Belgian Embassy rounded off the London visit, where the royals met William Hague and the Secretary of State for Foreign and Commonwealth Affairs.
They also squeezed in a visit to Westminster, where they met parliament leadership and the chairmen of the House of Commons and House of Lords.
The Belgian king and queen have recently started making their first official visits to European neighbours following Philippe's inauguration last July.
They have enjoyed lunch at the Élysée Palace with President Francois Hollande, visited King Willem-Alexander and Queen Maxima in The Hague, met German President Joachim Gauck at the Bellevue Palace in Berlin and Italian President Giorgio Napolitano at Quirinale Palace in Rome.