“greatly, yes, greatly.” The Hebrew text repeats the word “greatly” twice in succession at the end of the verse. This is the figure of speech epizeuxis, and emphasizes “greatly.” We might say something like, “exceedingly greatly.”
This kind of historically verifiable prophecy is one of the reasons that we know the Bible is true. The Bible is the only holy book with any clear and unmistakable prophecy that has been shown in history to come true. Unlike the Greek oracles which were so obscure that they had to be fit to the facts after the event, the Bible says over and over—in very clear language—what will happen in the future, but that future is past to us today so we can verify the prophecy. Who would have thought that about 4,000 years ago a man with a barren wife would become so numerous and so famous that the majority of the people on planet earth knew his name? Only the true God can foretell like that.