integrating networks

I would like to know what is the most secure way to connect networks that are independently managed. The senario is: A corporation has different departments. Each department has their own applications and independent network. But the CEO wants to have access to the applications on both networks. The network administrators are concerned on security. I thought about putting a router in the middle to connect to the switch from each network and only allowing the IP of the CEO’s computer(which ison one swich). Please give me any suggestions.