You and your great-great-great-great-grandfather's great-great-great nephew are fourth cousins, twice removed.
none of your great grandmas business
Fourth Cousins, twice removed
If there were no cousin marriages in his ancestry, George Washington had 256 great great great great great great great grandfathers. It is likely that no one knows who most of them were.
Your great-great-great uncle's great-great grandchild is your third cousin, once removed.