Corruption, masked in flattery, disheartened the king (12)

I believe the answer is:
adulteration
'corruption' is the definition.
(I've seen this before)
'masked in flattery disheartened the king' is the wordplay.
I cannot really understand how this works, but
'the' could be 't' (the is pronounced as a 't' sound in some dialects) and 't' is present in the answer.
'king' could be 'er' (abbreviation for Edward Rex, various English kings) and 'er' is present in the answer.
'flattery' could be 'adulation' (I've seen this in another clue) and 'adulation' is located in the leftover letters.
This accounts for all the letters.
This may be the basis of the clue (or it may be nonsense).
Can you help me to learn more?
(Other definitions for adulteration that I've seen before include "pollution" , "Corruption" , "Debasement" .)
