Book about a priest who finds a kid in a cave with some kind of amulet or talisman and adopts him. The kid later on turns out to be evil of some sort.

[Ivan]

Book about a priest (or at the very least someone involved with the church) who is on a missionary work or something like that and finds a young kid in a cave holding some sort of amulet or talisman, and decides to adopt the kid.

I read the book about 10 years ago (more or less) and the details are a bit fuzzy, but I remember that the kid (who is older now) turns out to be evil, tries to kill the priest who adopted him. For some reason I kind of remember that the kid ended up becoming the pope or something like that (???) and he was the antichrist or was attempting to prepare the world in order to bring the antichrist. I remember at least a part of the story is settled in Rome (?) or some other part of Italy.

Please keep in mind I don't really trust my memory and I've had no luck in finding the book for the last five years or so. I was merely 13 years old when I read it and cannot remember the exact details.