DidFocus with nested router?

[zackify]

I have a nested router that goes away on pressing a button. This causes the main router to come back into focus. There doesn't seem to be a hook for this. DidFocus doesn't get called because I guess technically it's still in focus, just behind the current navigator? If I'm wrong let me know. Would love to have a good way to know when a router comes back into focus from something like this.