If a game that was never announced gets cancelled, would anybody hear about it? The answer is yes, if someone tells the media.
Multiple unnamed sources have informed Kotaku that Eidos Montreal, the developer of Deus Ex: Human Revolution and the upcoming Thief title, has cancelled a third, unannounced game that was being worked on. One source said the game was a new IP, while two of those sources said that the title was connected to the Japanese branch of Square Enix, Eidos' parent company. The news of this cancellation comes out just days after Lightning Returns: Final Fantasy XIII gameplay director Yuji Abe suggested Eidos could be tapped to make a Final Fantasy game, which makes that quote sound a bit awkward (though the cancelled game may have had no connection to Final Fantasy).