Donald Lupton, History of Modern Protestant Divines (1637), pp. 358-360:
I have heard it confessed of English Papists themselves, which have been in Italy with [Cardinal Robert] Bellarmine himself, that he procured the true portraiture and effigies of this Whitaker to be brought to him, which he kept in his study. For he privately admired this man for his singular learning and ingenuity; and being asked of some of his friends, Jesuits, why he would have the picture of that heretic in his presence? he would answer, Quod quamvis haereticus erat et adversarius, erat tamen doctus adversarius: that, "although he was an heretic, and his adversary, yet he was a learned adversary."