Piece about king's nationalist policy (6)

I believe the answer is:

brexit

'nationalist policy' is the definition.
(the UK's exit from the European Union)

'piece about king's' is the wordplay.
'piece' becomes 'bit' (bit is a kind of piece).
'about' indicates putting letters inside.
'king' becomes 'rex' ('king' in Latin).
'bit' placed around 'rex' is 'BREXIT'.

I've seen this clue in the Sydney Morning Herald.

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