XenServer - exit full-screen with ctrl-alt

I just had some hard minutes searching for this:
In a Toolwire Training session (BTW: I hate them, they are requesting me to enter windows share pathes, but the java applet for the remote console doesn't accept my \ - so I had to copy it from an file explorer window - how ugly is that? they do not like german keyboards I guess - so they are not interested in the money of the german customers...) for my citrix xenserver certification, I clicked the "fullscreen" button to get the console of the running vm - by reflex, and so fast that I couldn't read the text on the button with the keyboard combination to get out again...

So, after searching (which didn't help, so with this entry google might help all other after me) for the and trying to figure the xenservcer exit fullscreen key combinations, I know in the end: it's ctrl-alt! Somehow I remember that from qemu, but I was sure I tried it sometimes before, until it finally worked...