Integrate an MS Exchange Calendar in your Google Calendar App (Android)

If you are in the situation that you want to use Google Calendar on an Android phone and you are not able to make the App show calendars from your Microsoft Exchange Server then you are just at the spot where I was.

I was surprised how hard it was to find a solution for this.
Eventually you tried one of those things:

1. Adding your Exchange Account to your Android Phone via main settings
2. Adding your Exchange calendars via your Google Calendar App
3. Trying weird work arounds to integrate the Exchange Calendars in your Google Calendar - and booy those companies make it tough to do just that

I hate long reads for simple questions, so here is the solution that worked for me:

Add your Exchange Account via the Gmail App on your phone.
Zuuup your calendars should show up in your Google Calendar App.

Downside: You are granting the Exchange server and thus the administrator quite severe access privileges to your phone. I'll leave the details to inform you about this to Google and the decision if you are willing to pay the price up to you.