So i was farming heralds in A1 blood moor and den, i was under the impression that in order to get the herald to spawn it has to be through the conversion of a champion pack.... well i drew the ire and walked into the den and turned a random monster into a herald. So confirmed once you draw the ire it doesn't have to be from a champion at all?

killing the champions or unique is what draws the ire, after that any newly activated monster even normal ones can become herald