At 11 o’clock on the night of 21 June  a dirty travelling-coach rolled into St James’s Square and came to a halt outside No. 18. Passers-by stopped and stared with curiosity at two military colours, their staffs topped with gilded Napoleonic eagles, which protruded from one of the coach windows. Its occupant, Major Henry Percy, one of Wellington’s aides-de-camp, alighted and bounded up the steps of Castlereagh’s house. On being informed that the Foreign Secretary was dining with Mr Edmund Boehm at No. 16, along with the Prince Regent and Lord Liverpool, Percy seized the two French colours and went to find him there. A moment later he burst into the dining room, threw the colours at the feet of the Prince Regent and announced that Wellington had won a great victory over Napoleon, who had fled the field followed by the remnants of his shattered army. Before he had finished telling the assembled company the glorious news a crowd had gathered outside, and the Prince Regent came out onto the balcony. Percy unfurled the captured French colours while the throng below sang ‘God Save the King’.
— Rites of Peace: The Fall of Napoleon and the Congress of Vienna by Adam Zamoyski