This is not an April Fool's joke. This really happened. In my Italian class we are studying holidays, and la Festa della Liberazione was on the agenda. My prof actually, in real life, said that day celebrates the day they threw out their German conquerors. WW2 is not my field but sometimes I have to teach World History and I have never before heard this put this way. Italy was a German ally, right? Does Italy have an alternate narrative? Is my prof nuts? What's going on?
Italy signed an armistice with the Allies on September 3, 1943 after the invasion of Sicily, after which Germany occupied Italy while the Allies fought their way up the mainland peninsula, capturing Rome on June 4, 1944 (two days before the Battle of Normandy began). Mussolini was deposed by the King of Italy and put under house arrest, but was later liberated by German special forces and put in charge of a puppet state in northern Italy, the Italian Social Republic. During this time, Mussolini's forces fought alongside the Germans, Italian partisan fighters - largely communists - fought against the Germans in occupied territory, and the Kingdom of Italy fought alongside the Allies and declared war on Germany. Mussolini was deposed again and publicly executed by partisans on April 28, 1945, two days before Hitler's suicide. German forces in northern Italy continued to fight against the Allies right up until Germany's surrender on May 8, 1945.
To answer your question specifically, "[la Festa della Liberazione](http://en.wikipedia.org/wiki/Liberation_Day_(Italy)" appears to celebrate the liberation of Turin and Milan by the Allies (possibly by partisans?) on April 25, 1945.