My maternal grandfather (born in Canada to English parents) was fond of saying, "I'm not English, I'm Irish!" As a result, my mother and her sisters grew up believing they were part Irish.
I know now (through my research) that I'm part Irish through my father's side of the family, but I've really struggled to find the Irish connection on my mother's side.
After a lot of determined digging, I discovered that one of my maternal grandfather's g-g-grandfathers was Jewish, but that can't be what he meant. Jewish/Irish... po-tay-to/po-tah-to... naaaaah.
Since then, I've found potential g-g-grandparents for him that might have an Irish connection or descent but I've been unable to prove it. The relevant church records (for England) weren't online the last time I checked, and I've purchased documentation on siblings, etc., looking for witnesses to events, all to no avail. (None of them had money or status, they moved around, they don't seem to have run afoul of the law, they died young, they left no wills.)
The potential g-g-grandfather was born in Oxfordshire but went to Dublin to enlist in 1802. Was there a familial reason why? His surname might have been Irish at some point. His wife had an Irish surname but I can't figure out where she was born (because of course I can't find them in the 1841 census and she died before the 1851 census was taken). They were married in England.
Anyway. Even if one of his g-g-grandmothers was Irish, or if both g-g-grandparents were of Irish descent, my grandfather was still mostly English, but I'll never be able to convince my aunts of that, LOL. (Not that I'd actually try, given that they are so firm in their belief.)