German runner in Heidelberg (4)

I believe the answer is:

elbe

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

'german runner' is the definition.
'Elbe' can be an answer for 'runner' (river in Germany). I'm unsure of the 'german' bit.

'in heidelberg' is the wordplay.
'in' indicates the answer is hidden within the clue.
'ELBE' is hidden within 'heidelberg'.

Can you help me to learn more?

(Other definitions for elbe that I've seen before include "German banker" , "A major German river" , "Dresden/Hamburg river" , "River of Germany" , "Flower" .)

I've seen this clue in The Sun.

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