Citation Hunt

The Wikipedia snippet below is not backed by a reliable source. Can you find one?

Click I got this! to go to Wikipedia and fix the snippet, or Next! to see another one. Good luck!

In page Frederick I of Prussia:

"

He also had an official mistress, Catharina von Wartenberg, between 1696 and 1711. However, he was never known to make use of her services, being deeply in love with his second wife.[citation needed]