Albert Barnes Commentary 2 Kings 19:9

"And when he heard say of Tirhakah king of Ethiopia, Behold, he is come out to fight against thee, he sent messengers again unto Hezekiah, saying," — 2 Kings 19:9 (ASV)

Tirhakah king of Ethiopia - This is the Tehrak or Teharka found in the hieroglyphics. He was the last king of the 25th (or Ethiopian) dynasty, which began with Shebek or Sabaco, and he reigned for over 26 years. The Assyrian inscriptions show that he still ruled in Egypt as late as 667 B.C., when Esarhaddon died and his son Asshur-bani-pal succeeded him (2 Kings 19:37).

He likely ascended the Egyptian throne around 692 B.C., having previously governed Ethiopia before he became king of Egypt . Thus, he was probably reigning in Ethiopia at the time of Sennacherib’s expedition, while Sethos and perhaps other secondary monarchs ruled over parts of Egypt. It was Tirhakah's movements that caused Sennacherib to send a second embassy instead of marching personally against the Jewish king.