(_London Gazette extraordinary._) “DOWNING-STREET, June 22d, 1815. “Major the Hon. H. Percy arrived late last night with a dispatch from field-marshal the duke of Wellington, K.G., to Earl Bathurst, his Majesty’s principal secretary of state for the war department, of which the following is a copy: _To Earl Bathurst._ “WATERLOO, June 19th, 1815. “MY LORD, “Bonaparte, having collected the 1st, 2d, 3d, 4th, and 6th corps of the French army, and the Imperial guard, and nearly all the cavalry, on the Sambre, and between that river and the Meuse, between the 10th and 14th of the month, advanced on the 15th, and attacked the Prussian posts at Thuin and Lobbes, on the Sambre, at day-light in the morning. “I did not hear of these events till in the evening of the 15th; and I immediately ordered the troops to prepare to march, and afterwards to march to their left, as soon as I had intelligence from other quarters to prove that the enemy’s movement upon Charleroi was the real attack. “The enemy drove the Prussian posts from the Sambre on that day; and general Zieten, who commanded the corps which had been at Charleroi, retired upon Fleurus; and marshal prince Blücher concentrated the Prussian army upon Sombreffe, holding the villages in front of his position of St.-Amand and Ligny. “The enemy continued his march along the road from Charleroi towards Brussels; and, on the same evening, the 15th, attacked a brigade of the army of the Netherlands, under the Prince de Weimar, posted at Frasnes, and forced it back to the farm-house, on the same road, called les Quatre-Bras. “The prince of Orange immediately reinforced this brigade with another of the same division, under general Perponcher, and, in the morning early, regained part of the ground which had been lost, so as to have the command of the communication leading from Nivelles and Brussels with marshal Blücher’s position. “In the mean time, I had directed the whole army to march upon les Quatre-Bras; and the 5th division, under lieutenant-general sir Thomas Picton, arrived at about half-past two in the day, followed by the corps of troops under the duke of Brunswick, and afterwards by the contingent of Nassau. “At this time, the enemy commenced an attack upon Prince Blücher with his whole force, excepting the 1st and 2d corps, and a corps of cavalry under general Kellermann, with which he attacked our post at Les Quatre-Bras.