Every story has its mystery. Even the ones that aren’t in that category. It’s what keeps the reader going.
The point is to wait until the right time for the big revelation. Most of the time it’s toward the end.
The reader can’t wait for it. It’s what they’re reading for. They want to know who the real villan’s been all along. They want to know who’s been leaving secret messages. Who’s going to end up with who? They’re waiting to be wowed.
There are so many events that happen before the big reveal, each building enthusiasm for it more and more.
If the reader has stayed through the ongoing events, they want to finish reading the story and that in itself is support. So, in a way, the story is all about the revelation, because writing is meant to give that wow factor and if you can give it. Give it.