BTB Alter Ego

During a BTB campaign, I was wondering whether or not players are supposed to know who or what the alter ego model is? It seems like alter ego is a really hard rule to play without everyone knowing who the alter ego is after the first round. What has everyone's experience with this rule been?

Here is the Rule:
Alter Ego: A randomly selected Hero (not a leader) from a randomly selected warband has begun working incognito with the opposition. Wearing a simple disguise, this traitorous individual is added to this warband’s roster as a Hired Sword with no upkeep cost. This is in addition to remaining a Hero in the starting warband. While incognito, the Hired Sword does not gain experience or become injured and the model carries the same equipment, adhering to all of the same requirements of his Hero alter ego. Any injuries, skills, equipment acquired or lost by the Hero will affect the Hired Sword alter ego. If at any stage the model is killed then remove the character from both warbands rosters. Note that in battles against the original warband the Hired Sword will work only as the Hero in the starting warband to hold up the double-cross.

Reference - BTB page 44

Yeah. It is not something that can be kept hidden. It doesn't really matter though that all warbands know who the alter ego is. The alter ego cannot fight against the warband in which it is a Hero so the original warband has no real reason to do anything drastic to the alter ego Hero. Hopefully a *strong* random hero is chosen as the alter ego as that would make the other warband even less likely to drop the Hero or take away all but a basic supply of equipment. Really it is just a (hopefully) strong, free warrior for the warband receiving the alter ego for hopefully more than the first battle.

We haven't got this far in our BTB campaign yet so I have yet to see it work in practice.