It apparently happened on Saturday (Japan time). Nintendo hasn't made a formal public announcement, but a release has been put out in both Japanese and English on the business side.
Nintendo is losing alot of their former presidents. It's a sad day for the game industry and sadly a lot of newer gamers won't know of his impact on the industry. Nintendo has put out a press release PDF out on their website about it. http://www.nintendo.co.jp/ir/pdf/2015/150713e.pdf