The prediction that the "last pope" will live during the closing days of the Catholic Church was made in the 12 century by the Irish bishop Malachy.
But Malachy did not say this pope would be bad.  He left that open.  What he did predict was a great struggle and defeat of the Catholic Church, including its end, and the coming of God's judgment.   By his words, the pope could even be a good man caught in a wicked struggle.

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And what if "Peter the Roman" is NOT the biggest and baddest cardinal, but someone trying his utmost to make things right in a dark world?
All I'm saying is, there is nothing in the prophecy which makes the last pope out to be a "false prophet."  He might be that, but not in St. Malachy's view.

 
St. Malachy's prophecy is not foolproof nor always precise.  It's not the Bible where we have, in St. Peter's words,
a "surer word of prophecy."