Deceitful person cheers king retreating (3)

I believe the answer is:

rat

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'deceitful person' is the definition.
'rat' can be an answer for 'person' (rat is a kind of person). I'm not certain of the 'deceitful' bit.

'cheers king retreating' is the wordplay.
'cheers' becomes 'ta' (both can informally mean thank you).
'king' becomes 'r' (abbreviation for rex, king in Latin).
'retreating' says the letters should be written backwards.
'ta'+'r'='tar'
'tar' in reverse letter order is 'RAT'.

Can you help me to learn more?

(Other definitions for rat that I've seen before include "Domestic rodent" , "one who betrayed" , "Treacherous person" , "one not going down with ship" , "Tell-tale" .)

I've seen this clue in The Times.

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