First of all you are talking about a 'NAT router'. A 'router' is something completely different.
Second, your server runs on the 192.x.x.x IP. So that is why it shows that IP...pretty simple. The server does not know anything about the external IP.
Somehow I'm guessing that this is not a dedicated server located in a hosting facility. But if it is...get some more IP's and get rid of that router.
The less-than-ideal solution is to buy another public IP, plug a switch into your modem, and then plug your server into the switch, and your NAT router into the switch as well. This way you still have your NAT network, but your server will have a public IP.