Sounds like Tim LaHaye's (spit!) theory. In his abominably bad Left Behind books, he makes the Tribulational pope named Peter, and aligned with Anti-christ.
His basis for this is half Malachi Martin and half Dave Hunt's bastardization of Revelation 17. LaHaye's acolytes will have a field day with this one.
St. Malachy is not related to Malachi Matrin. St. Malachy is a 12th century (?) mystic; Malachi Martin was a 20th century exorcist.