You need to install VirtualBox Extension Pack.
Download the file
Oracle_VM_VirtualBox_Extension_Pack-*.*.*.vbox-extpack, and double click to install it.
settings (of you
Display -> Remote Display -> Enable Server. Leave server port as
Null: no username required
External: use host user credential (
Windowsfor my case)
In Win10, click
Search and type
mtsc. Click on
Remote Desktop Connection.
Computer, put in
Authentication=External, put your Windows username and check
Allow me to save credentials(NOTE: this is a must).
If your VM guest support multiple monitors (
Settings -> Display -> Screen -> Monitor Count = 2), you can connect to the second monitor by using
NOTE: VirtualBox remote desktop share the same desktop as your client vm. If you want a separate independent desktop, you need to setup a remote desktop server on the client vm, such as Lubuntu Setup Remote Desktop With Xrdp.