Blunder hidden by my being bright and cheerful (5)

I believe the answer is:

merry

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

'blunder hidden by my' is the wordplay.
'blunder' becomes 'err' (I've seen this before).
'hidden by' means one lot of letters goes inside another (inserted letters are hidden inside).
'err' placed inside 'my' is 'MERRY'.

'being bright and' is the link.
This may not be correct. Some or all of it may belong to another bit of the clue.

Can you help me to learn more?

(Other definitions for merry that I've seen before include "Drunk - happy" , "Joyous, cheerful" , "Fjull of fun and gaiety" , "Lively -- slightly drunk" , "Mistresses Page and Ford of Windsor" .)

I've seen this clue in the Evening Standard.

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