On August 15, 1940, Italy attacked Greece

Hostilities opened between Italy and Greece with the torpedoing of the Greek cruiser Helle on August 15, 1940. The Greeks suspected an Italian submarine, but had no proof. General Metaxis asked what help Greece could expect from Great Britain on August 22. At that date, Britain didn't have any available forces to deploy to Greece. British forces, such as they were, were committed to defending Egypt. The actual Italian invasion was delayed, while they inquired what the German reaction would be. The Italian note was only delivered on October 28, 1940. Within hours, Greece and Italy were at war "through no fault of her own". This based on the account in the British Official History.