Was He Speaking Ex Cathedra?

Gregory the Great (Pope?) writes: "Ego autem fidenter dico, quia quisquis se universalem Sacerdotem vocat, vel vocari desiderat, in elatione sue Antichristum praecurrit, quia superbiendo se caeteris praeponit. Nec dispari superbia ad errorem ducitur, quia sicut perversus ille Deus videri vult super omnes homines; ita quisquis iste est, qui solus Sacerdos appelari appetit, super reliquos Sacerdotes se extollit."

Which roughly translates: "Therefore I fully affirm that whoever calls himself the universal Priest, or wants to be called that elevates himself to Antichrist, because he vaunts himself over all the others. Not only does this extreme arrogance lead to error, it's also perverse since this person wants to be seen as God over all people; thus whoever he is, who wants to be called the Priest alone, he exalts himself over all the other priests." (Cited in Principle of Protestantism, 169 -- Feel free to correct my translation if it needs it.)

One postscript to this quotation: This is an example of the medieval and patristic pedigree of Protestantism. It wasn't like Luther and Calvin came along and decided they really didn't like the Pope, flipped through their Bibles till they came to a bad name to call him, and them slapped "Antichrist" on the Papal See. They were in good catholic company calling the office of the "universal bishop of the Church" Antichrist. It was at least part of the teaching of the fathers.