If your 2xg-grandfather is the grandfather of your match, he would be your half first cousin twice removed.
If your great-grandfather is the grandfather of your match, he would be your half first cousin once removed.
If your great-grandfather's brother is the grandfather of your match, he would be your second cousin once removed.
The only one of these which comes up in the DNA Painter list is the second of those three, but it says "this relationship has a positive probability for 520cM in thednageek's table of probabilities, but falls outside the bounds of the recorded cM range (99th percentile)".
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