It was about three o'clock in the afternoon of the 15th, that a Prussian officer reached Brussels, whom General Ziethen had sent to Muffling to inform him of the advance of the main French army upon Charleroi. Muffling immediately communicated this to the Duke of Wellington; and asked him whether he would now concentrate his army, and what would be his point of concentration; observing that Marshal Blucher in consequence of this intelligence would certainly concentrate the Prussians at Ligny. The Duke replied - "If all is as General Ziethen supposes, I will concentrate on my left wing, and so be in readiness to fight in conjunction with the Prussian army. Should, however, a portion of the enemy's force come by Mons, I must concentrate more towards my centre. This is the reason why I must wait for positive news from Mons before I fix the rendezvous. Since, however, it is certain that the troops MUST march, though it is uncertain upon what precise spot they must march, I will order all to be in readiness, and will direct a brigade to move at once towards Quatre Bras." [Muffling, p. 231.]

Later in the same day a message from Blucher himself was delivered to Muffling, in which the Prussian Field-Marshal informed the Baron that he was concentrating his men at Sombref and Ligny, and charged Muffling to give him speedy intelligence respecting the concentration of Wellington. Muffling immediately communicated this to the Duke, who expressed his satisfaction with Blucher's arrangements, but added that he could not even then resolve upon his own point of concentration before he obtained the desired intelligence from Mons. About midnight this information arrived. The Duke went to the quarters of General Muffling, and told him that he now had received his reports from Mons, and was sure that no French troops were advancing by that route, but that the mass of the enemy's force was decidedly directed on Charleroi. He informed the Prussian general that he had ordered the British troops to move forward upon Quatre Bras; but with characteristic coolness and sagacity resolved not to give the appearance of alarm by hurrying on with them himself. A ball was to be given by the Duchess of Richmond at Brussels that night, and the Duke proposed to General Muffling that they should go to the ball for a few hours, and ride forward in the morning to overtake the troops at Quatre Bras.

To hundreds, who were assembled at that memorable ball, the news that the enemy was advancing, and that the time for battle had come, must have been a fearfully exciting surprise, and the magnificent stanzas of Byron are as true as they are beautiful; but the Duke and his principal officers knew well the stern termination to that festive scene which was approaching. One by one, and in such a way as to attract as little observation as possible, the leaders of the various corps left the ball-room, and took their stations at the head of their men, who were pressing forward through the last hours of the short summer night to the arena of anticipated slaughter.