Eastern European returning from Breslau (4)

I believe the answer is:

serb

I'm a little stuck... Click here to teach me more about this clue!

'eastern european' is the definition.
(I've seen this in another clue)

I cannot understand how the remainder of the clue works.

Can you help me to learn more?

(Other definitions for serb that I've seen before include "Balkan native" , "A European national" , "Native of the Balkans" , "One from Belgrade" , "Eastern European" .)

I've seen this clue in the Evening Standard.

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