This is a brief lexical note.
Revelation 17:11 uses the cardinal number ἑπτά, hepta (“seven”) and not the ordinal number ἕβδομος, hebdomos (“seventh”). So the eighth king will come “from (or of) the seven” and not “from the seventh.”
καὶ τὸ θηρίον ὃ ἦν καὶ οὐκ ἔστιν καὶ αὐτὸς ὄγδοός ἐστιν καὶ ἐκ τῶν ἑπτά [seven] ἐστιν, καὶ εἰς ἀπώλειαν ὑπάγει. (Rev 17:11)
“The beast who once was, and now is not, is an eighth king. He is of the seven and is going to his destruction.” (Rev 17:11)
I hope this lexical note is helpful for anyone studying this topic on the origin or nature of the eighth king, because this distinction will have implications for one’s study on this topic.