Sworn enemy.

There's a small trick against this... Attack with an empty hero (with 1 unit)... All the bonuses will be removed, as they only last for one battle.

It might also happen that there won't be a secondary hero nearby, or I'll drag a secondary hero to my main hero to gain an advantage over you. In short, it's impossible to say for sure what will happen.
P.S.: We seem to be getting off-topic.