A German river? (4)

I believe the answer is:

avon

'river?' is the definition.
(I know that Avon is a river)

'a german' is the wordplay.
'german' becomes 'von' (common element in German surnames).
'a'+'von'='AVON'

(Other definitions for avon that I've seen before include "River flowing through Shakespeare's Stratford" , "runner" , "Name of three English rivers" , "English river name in multiple use" , "River flowing through Bristol to the Severn" .)

I've seen this clue in the Evening Standard.

Want a hint initially instead of a full solution? Install my app