I believe the original prophecy of Malachy may have been accurate in listing only 111 Popes.  However, Peter the Roman could very well just be the leader of the Church, not officially the "Pope." During the conclave to elect a new Pope, the duties will be assumed by the current Camerlengo until the new Pope is in place. The current Camerlengo is a Roman whose full name is Tarcisio Pietro Evasio Bertone!  I'm fairly certain that "Pietro" is a variation of "Peter."

-Patty