>>You never know with nicknames.

Well, family names are even weirder.

Mine, Fitzgerald, is generally considered to Irish and all four of my grandparents did in fact come from County Kerry in Ireland.. but...
Gerald evolved from Gerardini.. some Roman fella who really was busy in the British Isles while the Romans occupied them. (maybe the word "romantic" was aimed at Signor Gerardini!)
We can only wonder where his ancestors came from.
Fitz is a Germanic form of Fils - the French word for Son used in Ireland during the Norman Occupation.

Quite a mishmash!