I'm trying to wrap my head around this, but I have no clue what's right. Maybe it would just be classified as "no relation", but that seems wrong to me.
The situation is that you have a grandfather, who remarries. I think that would be a step-grandmother, but I'm not even confident about that. It seems like a step-grandmother would actually imply that you have a step-mother or step-father, and it was their grandmother.
But if that's right, then would the "step-grandmother's" brother be called a "step-great-uncle", but that doesn't really capture the relationship either.
Can anyone supply an appropriate term?