User blog comment:Jopjopjop/Volume 19 Spoilers/@comment-68.53.63.249-20141130210927/@comment-24502975-20141130221947

I can confirm that it's stated in the volume 19 Afterword.

Speaking of which, it looks like Ishibumi also confirmed in it that the rest of the Evil Dragons  that we haven't seen yet will be revealed (I think Níðhǫggr is the only one that hasn't been mentioned yet).