[Mrs. Don-o]

OK, got that part. But who -— what person or body -— in the Church can declare it?

[piusv]

It appears that the question of a heretic pope came up at the First Vatican Council in 1870. When asked about this, Archbishop John Baptist Purcell related the following:

The question was also raised by a Cardinal, “What is to be done with the Pope if he becomes a heretic?” It was answered that there has never been such a case; the Council of Bishops could depose him for heresy, for from the moment he becomes a heretic he is not the head or even a member of the Church.