Xerneas and Yveltal were featured towards the end of the announcement trailer.
Pokemon X Version and Pokemon Y Version will each feature a new Legendary Pokemon, confirmed as Xerneas and Yveltal.
Xerneas – pronounced ZURR-nee-us – will feature in Pokemon X, whilst Yveltal - pronounced ee-VELL-tawl – will make an appearance in Pokemon Y.
The two characters made a brief appearance towards the end of yesterday's announcement trailer.
Pokemon X and Pokemon Y will launch worldwide for 3DS in October.
Source: Press release