All credits go to these sites : http://www.newsoflegends.com/ and http://www.surrenderat20.net
A video popped up on Tudou that looks to be a new champion teaser. Note that this is purely speculative and the video could be teasing something else (perhaps new Shadow Isles lore?)?
[ EDIT ] Looks like it’s officially confirmed and the video is now up on Riot’s channel:
On Reddit, the Champion’s name was roughly translated to Tamm, King of the Rivers. (again, unconfirmed).
Here are some screenshots I took from the video: