Belgium was liberated late in 1944 by Allied forces, including British, Canadian, and American armies. Leopold III's brother, Charles, the Count of Flanders, was appointed Regent, pending a decision about whether the King would be able to regain his former position on the throne. In February 1945, Achille Van Acker replaced Pierlot as Prime Minister. The resistance was disarmed, and many of its members and other Belgians who had remained in the country during the occupation were mobilised into the regular Belgian army in 57 "Fusilier Battalions". These battalions served in several battles on the western front. 100,000 Belgians were fighting in the Allied armies by VE Day.
General Courtney Hodges' U.S. First Army liberated the region south of Brussels and Maastricht in early September 1944. While two corps of the First Army were concentrated elsewhere, VIII Corps occupied a long stretch of the front from the area south of Liège, across the Ardennes and into Luxembourg. The length of the deployment meant that the Corps' front line was only lightly defended, leaving it vulnerable.
Following a few months of relative calm in Belgium, on 16 December 1944 the Germans launched the Ardennes Offensive with over a quarter of a million soldiers. Antwerp was the ultimate objective of the German offensive, but the German advance stalled before the Meuse River, at Celles near Dinant, and was pushed back in furious fighting over a period of six weeks in bitterly cold weather by American, British and Belgian troops. Belgian towns and civilians in the Ardennes suffered during the offensive as homes were reduced to ruins, and there were instances of German troops shooting civilians. Around 90% of the town of La Roche-en-Ardenne was destroyed during fighting. By 4 February 1945, the country was reported to be free of German troops.
In the six months following Allied liberation, Belgian towns were widely targeted by the unpiloted German V-Bombs. A total of 2,342 of these rockets (mostly of the more advanced V-2 type) fell in a 10-mile radius around Antwerp alone. A post-war SHAEF report estimated V-Bombs had been responsible for killing 5,000 people and injuring a further 21,000, mostly in the cities of Liège and Antwerp.
The period after liberation also saw a wave of prosecutions of those suspected of collaboration during the war. 400,000 Belgians were investigated for collaboration of whom 56,000 were prosecuted. Nearly 250 were executed. Léon Degrelle, despite being sentenced to death, managed to escape to Francoist Spain, where he remained until his death in 1994.