Animal to upset King Arthur's city (7)
I believe the answer is:
camelot
'city' is the definition.
(I have seen 'Fabulous city' mean 'camelot' so perhaps 'city' could also mean 'camelot')
'animal to upset' is the wordplay.
'animal' becomes 'camel' (I've seen this in other clues).
'upset' is a reversal indicator.
'to' in reverse letter order is 'ot'.
'camel'+'ot'='CAMELOT'
'king arthur's' is the link.
This may not be correct. Some or all of it may be part of another bit of the clue.
Can you help me to learn more?
(Other definitions for camelot that I've seen before include "King Arthur's court - or JFK's" , "Place where King Arthur held court" , "Mythical British kingdom" , "royal court" , "King Arthur's kingdom - or JFK's" .)