How to add Windows 2012 R2 RDS to Existing Windows 2008 R2 Terminal Server

I currently have a Windows 2008 R2 Terminal Server running and I am looking to add a Windows Server 2012 R2 server to it. All I see when I google the setup is only for Windows Server 2012 R2 RDS, cant find anything to integrate with a current 2008 R2 Terminal Server.

Can anyone help with this or point me to a blog I possibly missed?

Thanks.