Behold, I will send a blast upon him, and he shall hear a rumour, and shall return to his own land; and I will cause him to fall by the sword in his own land. Behold, I will send a blast - and he shall hear a rumor - The rumor was, that Tirhakah had invaded Assyria. The blast was that which slew one hundred and eighty-five thousand of them in one night, see 2 Kings 19:35.
Cause him to fall by the sword - Alluding to his death by the hands of his two sons, at Nineveh. See 2 Kings 19:35-37.