To not bring it up at all feels deceitful given the nature of the situation, even if there is no outright lying done, particularly when now knowing it will surely change our friendship in all kinds of ways. I don't like the idea of us not being on even ground.

This friend has brought up the topic, hinted at it, previously (and each time only when drunk, for what that's worth). As a result we have talked about it on occasion. The topic is fine, but the exact content... I suppose I could frame that in the sense of we've discussed a question or possibility, but it was only this recent conversation when my friend gave what seemed to be a very sure answer. Every other time my friend has said that it's is confusing at that point and we ought to talk about it later on.

My inclination is to do similarly to as Mr Silver suggested, to say, "hey, about that other night; you told me something quite significant and personal; do you want to know what you said/did?". And if my friend would rather leave it be without knowing what I know I won't bring it up again until the topic naturally resurfaces.