An all new type of Pokemon may be getting added into the upcoming Pokemon X & Y games. The reveal was made not through any official sources, but through renowned leaker @Hirobyte on Twitter, who stated that the legendary Xerneas and Sylveon Pokemon would be of this new type.
Additionally, he revealed that Yveltal will be a Dark/Flying type, will existing Pokemon that could very well fit into the Fairy type will be reclassified. These include Pokemon like Clefairy and Togetic.
The leaker, @Hirobyte, is well-regarded for his information in the Pokemon community due to revelations about Pokemon Black & White that ended up being true. He revealed the entire Pokedex of the aforementioned games ahead of the Japanese launch, with information that only could have been known to someone working in localization for Nintendo, or directly at GameFreak. It's probable that @Hirobyte is close to someone on the game's large staff.
It remains to be seen whether what he says is true, but given his past record, there's little reason to doubt the veracity of his claims.
Pokemon X & Y are slated for release later this year, on October 2013. The game is exclusive to the Nintendo 3DS.