Battle of Waterloo
Suddenly 1,500 British Foot Guards under Peregrine Maitland, who had been lying down to protect themselves from the French artillery, rose and devastated them with point-blank volleys. The chasseurs deployed to answer the fire, but some 300 fell from the first volley, including Colonel Mallet and General Michel, and both battalion commanders. A bayonet charge by the Foot Guards then broke the leaderless squares, which fell back onto the following column. The 4th Chasseurs battalion, 800 strong, now came up onto the exposed battalions of British Foot Guards, who lost all cohesion and dashed back up the slope as a disorganized crowd with the chasseurs in pursuit. At the crest the chasseurs came upon the battery that had caused severe casualties on the 1st and 2nd/3rd Chasseurs. They opened fire and swept away the gunners. The left flank of their square now came under fire from a heavy formation of British skirmishers, which the chasseurs drove back. But the skirmishers were replaced by the 52nd Light Infantry (2nd Division), led by John Colborne, which wheeled in line onto the chasseurs' flank and poured a devastating fire into them. The chasseurs returned a very sharp fire which killed or wounded some 150 men of the 52nd. The 52nd then charged, and under this onslaught, the chasseurs broke.
The last of the Guard retreated headlong. A ripple of panic passed through the French lines as the astounding news spread: "La Garde recule. Sauve qui peut!" ("The Guard is retreating. Every man for himself!") Wellington now stood up in Copenhagen's stirrups and waved his hat in the air to signal a general advance. His army rushed forward from the lines and threw themselves upon the retreating French.
The surviving Imperial Guard rallied on their three reserve battalions (some sources say four) just south of La Haye Sainte for a last stand. A charge from Adam's Brigade and the Hanoverian Landwehr Osnabrück Battalion, plus Vivian's and Vandeleur's relatively fresh cavalry brigades to their right, threw them into confusion. Those left in semi-cohesive units retreated towards La Belle Alliance. It was during this retreat that some of the Guards were invited to surrender, eliciting the famous, if apocryphal, retort "La Garde meurt, elle ne se rend pas!" ("The Guard dies, it does not surrender!").

Prussian capture of Plancenoit: At about the same time, the Prussian 5th, 14th, and 16th Brigades were starting to push through Plancenoit, in the third assault of the day. The church was by now on fire, while its graveyard—the French centre of resistance—had corpses strewn about "as if by a whirlwind". Five Guard battalions were deployed in support of the Young Guard, virtually all of which was now committed to the defence, along with remnants of Lobau's corps. The key to the Plancenoit position proved to be the Chantelet woods to the south. Pirch's II Corps had arrived with two brigades and reinforced the attack of IV Corps, advancing through the woods.
The 25th Regiment's musketeer battalions threw the 1/2e Grenadiers (Old Guard) out of the Chantelet woods, outflanking Plancenoit and forcing a retreat. The Old Guard retreated in good order until they met the mass of troops retreating in panic, and became part of that rout. The Prussian IV Corps advanced beyond Plancenoit to find masses of French retreating in disorder from British pursuit. The Prussians were unable to fire for fear of hitting Wellington's units. This was the fifth and final time that Plancenoit changed hands.
French forces not retreating with the Guard were surrounded in their positions and eliminated, neither side asking for nor offering quarter. The French Young Guard Division reported 96 per cent casualties, and two-thirds of Lobau's Corps ceased to exist.

Despite their great courage and stamina, the French Guards fighting in the village began to show signs of wavering. The church was already on fire with columns of red flame coming out of the windows, aisles and doors. In the village itself—still the scene of bitter house-to-house fighting—everything was burning, adding to the confusion. However, once Major von Witzleben's manoeuvre was accomplished and the French Guards saw their flank and rear threatened, they began to withdraw. The Guard Chasseurs under General Pelet formed the rearguard. The remnants of the Guard left in a great rush, leaving large masses of artillery, equipment and ammunition wagons in the wake of their retreat. The evacuation of Plancenoit led to the loss of the position that was to be used to cover the withdrawal of the French Army to Charleroi. The Guard fell back from Plancenoit in the direction of Maison du Roi and Caillou. Unlike other parts of the battlefield, there were no cries of "Sauve qui peut!" here. Instead, the cry "Sauvons nos aigles!" ("Let's save our eagles!") could be heard.

French disintegration: The French right, left, and centre had all now failed. The last cohesive French force consisted of two battalions of the Old Guard stationed around La Belle Alliance; they had been so placed to act as a final reserve and to protect Napoleon in the event of a French retreat. He hoped to rally the French army behind them, but as retreat turned into rout, they too were forced to withdraw, one on either side of La Belle Alliance, in square as protection against Coalition cavalry. Until persuaded that the battle was lost and he should leave, Napoleon commanded the square to the left of the inn. Adam's Brigade charged and forced back this square, while the Prussians engaged the other.
As dusk fell, both squares withdrew in relatively good order, but the French artillery and everything else fell into the hands of the Prussian and Anglo-allied armies. The retreating Guards were surrounded by thousands of fleeing, broken French troops. Coalition cavalry harried the fugitives until about 23:00, with Gneisenau pursuing them as far as Genappe before ordering a halt. There, Napoleon's abandoned carriage was captured, still containing an annotated copy of Machiavelli's The Prince, and diamonds left behind in the rush to escape. These diamonds became part of King Friedrich Wilhelm of Prussia's crown jewels; one Major Keller of the F/15th received the Pour le Mérite with oak leaves for the feat. By this time 78 guns and 2,000 prisoners had also been taken, including more generals.

There remained to us still four squares of the Old Guard to protect the retreat. These brave grenadiers, the choice of the army, forced successively to retire, yielded ground foot by foot, till, overwhelmed by numbers, they were almost entirely annihilated. From that moment, a retrograde movement was declared, and the army formed nothing but a confused mass. There was not, however, a total rout, nor the cry of sauve qui peut, as has been calumniously stated in the bulletin.
In the middle of the position occupied by the French army, and exactly upon the height, is a farm  [sic], called La Belle Alliance. The march of all the Prussian columns was directed towards this farm, which was visible from every side. It was there that Napoleon was during the battle; it was thence that he gave his orders, that he flattered himself with the hopes of victory; and it was there that his ruin was decided. There, too, it was that, by happy chance, Field Marshal Blücher and Lord Wellington met in the dark, and mutually saluted each other as victors.
Other sources agree that the meeting of the commanders took place near La Belle Alliance, with this occurring at around 21:00.

Aftermath: Waterloo cost Wellington around 17,000 dead or wounded, and Blücher some 7,000 (810 of which were suffered by just one unit: the 18th Regiment, which served in Bülow's 15th Brigade, had fought at both Frichermont and Plancenoit, and won 33 Iron Crosses). Napoleon's losses were 24,000 to 26,000 killed or wounded, including 6,000 to 7,000 captured with an additional 15,000 deserting subsequent to the battle and over the following days.

22 June. This morning I went to visit the field of battle, which is a little beyond the village of Waterloo, on the plateau of Mont-Saint-Jean; but on arrival there the sight was too horrible to behold. I felt sick in the stomach and was obliged to return. The multitude of carcasses, the heaps of wounded men with mangled limbs unable to move, and perishing from not having their wounds dressed or from hunger, as the Allies were, of course, obliged to take their surgeons and waggons with them, formed a spectacle I shall never forget. The wounded, both of the Allies and the French, remain in an equally deplorable state.