This question already has an answer here:
Why some titles like Astronomer Royal are styled that way?
What I mean is that usually, in English (and even in German and other Germanic languages, I suppose), the adjective is placed before the noun, so the most common form would be Royal Astronomer.
Placing the adjective after the noun is more common in Romance languages, like French or my own Italian (that in example would be Astronomo Reale).
I suspect that the reason is of contamination between languages, but are there other reasons why some titles use this particular styling, while other, even similar ones, like i.e. the Royal Astronomer of Ireland, use the more conventional way?
I'm interested in both answers that address the generic placement of adjectives after the nouns, and in the more specific history of the styling of the title Astronomer Royal itself.