Cad turned on queen and popular old king (7)

I believe the answer is:

tarquin

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'old king' is the definition.
(legendary king of Rome)

'cad turned on queen and popular' is the wordplay.
'cad' becomes 'rat' (I've seen this before).
'turned' says the letters should be written in reverse.
'on queen' becomes 'qu' (abbreviation for queen. I am not sure about the 'on' bit.).
'and' means one lot of letters go next to another.
'popular' becomes 'in' ('in' can mean trendy).
'rat' reversed gives 'tar'.
'tar'+'qu'+'in'='TARQUIN'

Can you help me to learn more?

(Other definitions for tarquin that I've seen before include "proud king" , "Last Etruscan king of Rome, 534-510 BC" .)

I've seen this clue in The Guardian.

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