Theatrical cover reveals have become common procedure in YA publishing, but Simon & Schuster Books for Young Readers put a, well, novel spin on its unveiling of the cover of Cassandra Clare’s Clockwork Princess, the final Infernal Devices book: the reveal was controlled by fans. Many thousands of them.

The cover of the March 2013 novel from Margaret K. McElderry Books, which has a million-copy first printing, was posted on the series’ Web site at 3:00 p.m. EDT on July 10, but it was hidden behind an ethereal veil that only tweeting readers could remove. For every tweet sent that included the hashtag #ClockworkPrincess, the veil was diminished, revealing the cover one shred at a time.

It didn’t take long for fans to complete the task. Immediately after the veiled cover appeared online, the publisher began the reveal challenge, which was announced through Clare’s Twitter, Tumblr, and Facebook channels. Tweets began to pour in instantly, and within two hours, fans had generated 30,000 tweets, the cover appeared in full view on the Web site, and #ClockworkPrincess was trending worldwide on Twitter. S&S posted a video on YouTube chronicling the progression of the gradual cover reveal.

But the tweeting didn’t stop once the cover was revealed. By 7:00 p.m., there were 100,000 fan-generated tweets as readers continued to express their excitement about the author, the Clockwork Princess cover,and the reveal process. One fan tweeted, “Over 51,000 tweets, we already have the cover, but we are still tweeting. I am so proud to be an ID fan!” Another insisted, “#ClockworkPrincess just made my life so complete right now. I want to attack the designers and Cassandra Clare with my love.” And from a third: “#ClockworkPrincess It’s done, not joking i would have tweeted all night if it needed 1,000,000 tweets.” Still growing, the tweet tally is currently approaching 160,000.

The cover reveal was masterminded by Matt Pantoliano, senior digital marketing manager of S&S’s Books for Young Readers. Noting that, to his knowledge, this reader-driven reveal is a first for book publishing, he explains that the promotion was somewhat inspired by the reveal procedure of a poster for a Batman movie several years ago. “It’s been in the back of my head for a while as a cool thing to do,” he says. “Cassie has a big following on Twitter, so we knew she’d be the right author to do this kind of reveal for.” And with 12 million copies of Clare’s Mortal Instruments and Infernal Devices novels in print, the author certainly has a sizable and widespread fan base.

Remarking that he and his colleagues are “gratified and very impressed” by the number of fans who participated and the speed with which the cover was revealed, Pantoliano says that the promotion was propitiously timed. “The City of Bones movie is coming out next year, and the poster art was revealed this week, so there was already a Cassie Clare frenzy in the works,” he says. “This cover reveal added fuel to the fire, and fans rallied together with so many calls to action. It was kind of a perfect storm of Cassie Clare.”