Crossword Genius

One sure to succeed Brown going up river (7)

Ross

I believe the answer is:

natural

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'one sure to succeed' is the definition.
I can't judge whether this defines the answer.

'brown going up river' is the wordplay.
'brown' becomes 'tan' (tan is a kind of brown).
'going up' is a reversal indicator (in a down clue, the letters are written upwards).
'river' becomes 'ural' (Russian river).
'tan' in reverse letter order is 'nat'.
'nat'+'ural'='NATURAL'

Can you help me to learn more?

(Other definitions for natural that I've seen before include "An ideal person" , "Unforced" , "Inborn, normal ( 7)" , "character on the staff" , "person regarded as certain to qualify" .)

I've seen this clue in The Telegraph.
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