Nintendo America announced the existence of GameCube Controller adapters via their official Twitter account. This will let players play the Smash Bros. using GameCube controllers on the Wii U.
Aside from the tweet, no other details have been divulged regarding the adapter. There's still no word on pricing details and how it will be sold. We will update this story as we know more in the future though. It'll be interesting to hear what other games are potentially compatible with the adapter.
Get excited! The #WiiU version of #SmashBros. will be playable with GameCube controllers. pic.twitter.com/nmyj9QMsuU
— Nintendo of America (@NintendoAmerica) May 29, 2014
The adapter was also teased at the end of the trailer for the Smash Bros. Invitational trailer. You can check that out below: