As promised, Nintendo announced a new addition to the Super Smash Bros. roster this morning. They actually ended up delivering more than that, though, with the return of Captain Falcon as well as more characters from Fire Emblem: Awakening.
Lucina and player avatar Robin (male and female versions) are all joining the lineup when Super Smash Bros. hits Nintendo 3DS this summer, followed by Wii U this winter.
UPDATE: Here's the video! (and Chrom is in the mix as an Assist Trophy, not playable)