Most intelligent, supreme? That's about right (9)

I believe the answer is:

brightest

'most intelligent' is the definition.
(I've seen this before)

'supreme? that's about right' is the wordplay.
'supreme?' becomes 'best' (I've seen this before).
'that's about' indicates putting letters inside.
'best' going around 'right' is 'BRIGHTEST'.

(Another definition for brightest that I've seen is " Most intelligent".)

I've seen this clue in The Guardian.

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