UPDATE: Phil Spencer said on Major Nelson's podcast that they will have a "unique exclusive" for Xbox One at Gamescom, and also said they'll have something to say about "Europe's biggest franchise." I'm not speculating.
Microsoft will be at Gamescom in force to showcase the Xbox One, with Phil Spencer delivering the keynote address and the company holding a pre-Gamescom event on Tuesday. We've heard before that they would be announcing a new title for the next-gen system, but now Microsoft has issued a statement to Gamespot declaring they will have "exciting news" to present. You'll be able to judge for yourself just how exciting it is, because there will be livestreams of everything.