User blog comment:Xilinoc/Ch. 542 - THE BLADE IS ME/@comment-11130627-20130621163942/@comment-11051098-20130621214022

Yes, from the little we saw, I think we're all sure that the mystic figure is Grimmjow. Also the way he spoke - or yelled - to Ichigo, that's another proof. I'm sure Kubo will confirm it soon enough.