Exceed one’s power, being open about English king (9)

I believe the answer is:

overexert

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'exceed one's power' is the definition.
I can't tell whether this definition defines the answer.

'open about english king' is the wordplay.
'open' becomes 'overt' (synonyms).
'about' is an insertion indicator.
'english' becomes 'E' (abbreviation).
'king' becomes 'rex' ('king' in Latin).
'e'+'rex'='erex'
'overt' going around 'erex' is 'OVEREXERT'.

'being' acts as a link.

Can you help me to learn more?

(Other definitions for overexert that I've seen before include "work too hard" , "strain" , "use too much" , "exercise unduly?" , "Make too much effort" .)

I've seen this clue in The Times.

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