Sillier daughter behind the Queen (6)

I believe the answer is:

dafter

'sillier' is the definition.

'daughter behind the queen' is the wordplay.
'daughter' becomes 'd'.
'behind' becomes 'aft' (synonyms).
'the queen' becomes 'er' (abbreviation for Elizabeth Regina).
'd'+'aft'+'er'='DAFTER'

(Other definitions for dafter that I've seen before include "More foolish!" , "crazier" .)

I've seen this clue in The Telegraph.

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