Well, I do not believe in any serb/sorb hidden history, but what Bosnak wrote about city Zerbst and Katy the Great is not completely without sense.

The name of the city Zerbst could have derive with high propability from slavic tribal name Serbs.
(in czech language the city is called simply Srbiště)
Like other slavic toponyms at that area like Plötzkau, Dessau. (Anhalt-Plotzkau, Anhalt-Dessau.)

Thus, The last part of the name of Katy the Great…Anhalt-Zerbst….could be of slavic origin.

But, there is nothing hiddden in it, I suppose.