Here's the letter
Translation
"I have received comments from various quarters regarding the "Manga Mangyo-ki" article that is being serialized in the Kumamoto Nichinichi Shimbun. I have made the definite statement that Yamato is to be added to the Straw Hat crew in "One Piece," but there is no basis for this statement. We have received inquiries about whether we are getting our information from somewhere, but that is never the case. It is based on my personal wish that Yamato will join us, based on my reading of the series so far. At the same time, it was premature to say that the 10th member of the group has been confirmed, which is a spoilerific expression. At this point, it has not been confirmed that Yamato will be Luffy's companion. I would like to take this opportunity to apologize for any inconvenience this may have caused."
Translation
"I have received comments from various quarters regarding the "Manga Mangyo-ki" article that is being serialized in the Kumamoto Nichinichi Shimbun. I have made the definite statement that Yamato is to be added to the Straw Hat crew in "One Piece," but there is no basis for this statement. We have received inquiries about whether we are getting our information from somewhere, but that is never the case. It is based on my personal wish that Yamato will join us, based on my reading of the series so far. At the same time, it was premature to say that the 10th member of the group has been confirmed, which is a spoilerific expression. At this point, it has not been confirmed that Yamato will be Luffy's companion. I would like to take this opportunity to apologize for any inconvenience this may have caused."