The episode showed the "dire consequences" that fake news can have, the Pope warned in a document.
Pope Francis also said it led only to the spread of arrogance and hatred.
Social media users and journalists should unmask manipulative tactics that foment division, he said.
The document The Truth Will Set You Free - Fake News and Journalism for Peace was issued ahead of the Catholic Church's World Communications Day on 13 May, and it was the first time the Pope has written on the topic.