I'd tell them, yes, but it wouldn't be the first thing that came out of my mouth.

I rarely even talk about exes to my current partner at all, so bringing them up just because they happened to be the same sex as me doesn't really make sense to me.
But like I said, I'd tell them soon enough, yes. It's not a secret or anything and if they can't handle the fact that I'm bi, I'd rather know sooner than later.