Upset concerning monarch’s seat, we hear (10)
I believe the answer is:
overthrown
'upset' is the definition.
(I've seen this before)
'concerning monarch's seat we hear' is the wordplay.
'concerning' becomes 'over' (both can mean relating to).
'monarch's seat' becomes 'throne' (I've seen this before).
'we hear' shows a homophone (sound like).
'throne' sounds like 'thrown'.
'over'+'thrown'='OVERTHROWN'
(Other definitions for overthrown that I've seen before include "Upset" , "deposed" , "Defeated" .)