Grandson of one's sibling or sibling's spouse, son of one’s nephew or niece, one's sibling's child's male child.(noun)
One's son’s or daughter's nephew.(noun)
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Use "great-nephew" in a sentence
"Dr.I. Milo Shepard, is a great-nephew of Jack London, and grandson of Eliza London Shepard, Jack London's stepsister and ranch superintendent."
"Unless you were talking about Aleksey Tolstoy, the minor writer and great-nephew of Lev."
"They're all overshadowed, really, by Octavian, the man who will become Caesar Augustus, the first true emperor, you know, Julius Caesar's adopted son, his real great-nephew."