Amazon just announced that author Nora Roberts has sold her one millionth ebook from Amazon’s Kindle store. “As of yesterday, Nora Roberts has sold 1,170,539 Kindle books…” Amazon wrote in their press release. But I’d already seen the signs. Last week Amazon had revealed the best-selling ebooks of 2010 — and four of them were written by Nora Roberts! “Nora Roberts has been a bestseller at Amazon for 15 years,” Amazon’s vice president of Kindle Content announced, “so this accomplishment is no surprise.”

The New Yorker calls her “America’s favorite novelist,” according to Amazon’s press release, and she’ll now join what Amazon calls the “Kindle Million Club.” She’s only the third author to ever sell this many ebooks from the Kindle store, since it was only July when Amazon announced that their Kindle store had its first million-selling author. (Ironically, the author was already dead, since the late Stieg Larsson’s “Girl with the Dragon Tattoo” trilogy had unexpectedly turned into three posthumous best-sellers). And it wasn’t until October that a second author achieved the same success — James Patterson — though that was probably inevitable. Wikipedia noted that he’d written 56 different books which were all best-sellers (which got him listed in the Guinness Book of World Records).

At the time I wondered if Patterson reached his million-book milestone simply by selling 20,000 copies of 50 different books — and now I’m wondering if Roberts had a similar advantage. To get to the one-million figure, Amazon included books which Roberts wrote under her pseudonym, J.D. Robb — which include a sprawling, 40-book series in which every title ends with the words “in Death.” (Naked in Death, Glory in Death…) In fact, Roberts has written more than 200 novels, according to Amazon’s press release. Even if she sold just 5,000 copies of each one, she’d still be able to pass the one-million sales milestone.

I’d also wondered if they included any free ebook downloads in their figures, but Amazon insists they’re only counting copies which were actually purchased. So this announcement may be just what it seems: still more proof of the tremendous popularity of ebooks. In November Amazon said that ebooks always outsell the printed books for the top 1,000 best-selling titles on the site. And earlier this month, USA Today announced that ebooks were also outselling the print editions for 19 of the top 50 books on their own best-seller list. (“It’s the first time the top-50 list has had more than two titles in which the e-version outsold print,” they reported last week.)

Of course, Roberts had already sold more than 280 million print editions of her books already, according to Wikipedia, spending a combined total of more than 660 weeks on the New York Times best-seller lists. And Roberts’ ebooks may have gotten a special boost from the Kindle, according to another new article in USA Today. They reported that romance novels accounted for 12% of all the best-selling books of 2010, theorizing that “Readers who wouldn’t be caught dead with risque covers in public enjoyed the privacy of reading romantic e-books!”

And what were Nora Roberts most popular ebooks of 2010?

The Search (her most popular ebook of the year)

Savor the Moment

Fantasy in Death (as J.D. Robb)

Happy Ever After