Crossword Genius

Where Walter was upset at getting a “pair” (8)

Ross

I believe the answer is:

waterloo

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

'where walter was upset at getting a pair' is the definition.
Although both the answer and definition are singular nouns, I can't understand how they can define each other.

'where walter was upset' is the wordplay.
'where' indicates an anagram (I've seen this in other clues).
'was upset' becomes 'oo' (I am not sure about this - if you are sure you should believe this answer much more).
'walter' is an anagram of 'waterl'.
'waterl'+'oo'='WATERLOO'

Can you help me to learn more?

(Other definitions for waterloo that I've seen before include "Famous battle" , "Wellington's victory" , "Historical action" , "Where Napoleon met his final defeat" , "6D 5A [TUBE STATION]" .)

I've seen this clue in the Evening Standard.
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