Configuring DNS to resolve root remotely and subdomain locally

Let's say I own the domain example.com, and have a website hosted on an exteal server at http://example.com, which is also accessible from http://www.example.com.

I want to run my local OwnCloud instance at http://cloud.example.com, which should be accessible both locally and remotely. To make this accessible via LAN in my own network, I set up a local BIND server which resolves cloud.example.com to the local IP address of the server. However, since this is the only server, browsing to http://example.com resolves to the same machine and not to the remote website.

How could I set up my BIND server to do the following?

• Accessing cloud.example.com from the LAN should resolve to a local IP
• Accessing cloud.example.com through the Inteet should work (will use dynamic DNS for this)
• Browsing to http://example.com or http://www.example.com from LAN or Inteet should display the exteally hosted website

I am fairly new to DNS implementations so happy to RTFM if needed. Thanks.