Is the phrase "Vicarius Filii Dei" grammatically correct?

Question

My Latin's a bit rusty, but if I remember the declensions correctly, shouldn't it be "Vicarius Filius Dei"? The phrase is to mean "Vicar of the Son of God", and since "Son" belongs to "God" it should take the genitive rather than the nominative, correct?

I was thinking about this yesterday after reading a chapter on Anti-Catholicism in the U.S. This phrase allegedly appears on Papal tiaras, although there don't seem to be any photos or other evidence of it.

Answer 1

Vicarius Filii Dei is correct.

Vicarius is nominative; Filii is genitive; Dei is genitive.

Vicarius Filius Dei would be nominative, nominative, genitive, which as you noted would be incorrect.

Answer 2

I'm sorry, I have a college degree, and I still say huh?  But I admire the fact that you are interested in this stuff :)