Catholic leader Pope Francis shocked worshippers at the Vatican on Sunday (02Mar14) when he accidentally swore during his weekly blessing.

The Argentinian pontiff, who was born Jorge Mario Bergoglio, was delivering his speech in Italian at the weekend when he used the word "cazzo", the equivalent of the 'f' word, in place of "caso", which means "case".

The 76 year old, whose native language is Spanish, quickly realised his error and corrected himself, but his mistake didn't go unnoticed.

Translated into English, the speech read: "If each one of us does not amass riches only for oneself, but half for the service of others, in this f**k... in this case the providence of God will become visible through this gesture of solidarity."

The embarrassing flub makes Pope Francis the first pontiff in history to ever let slip an expletive in public.