Do you tell a new partner before or after the first flare up?

I have been seeing someone for about two months and I have not said anything yet because I have not had an outbreak the whole time. Now I can feel one coming and I am panicking about whether to explain it now or wait until it is visible and just deal with it then. Part of me thinks bringing it up before there is anything to see makes it a bigger deal than it is, but the other part feels like hiding it is worse. How did you handle the timing with someone new?