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Most likely it's Frostfang), the dragon champion that Aesgir supposedly slew in one punch after obtaining the same jotun scroll Braham used to enchant his bow. The legendary axe is named after that dragon champion, which was said to be Jormag's mightiest champion (at the time/so far as of core).
Aesgir killed Frostfang on his way to battle Jormag, the latter battle we see via the vision took place at Aesgir's Legacy.
Ding ding ding!