Sunned part undoing briefs? (10)

I believe the answer is:

underpants

I'm a little stuck... Click here to teach me more about this clue!

'briefs?' is the definition.
Although both the answer and definition are nouns, they are not in the same form of the noun.

'sunned part undoing' is the wordplay.
'undoing' indicates an anagram.
'sunned'+'part'='sunnedpart'
'sunnedpart' anagrammed gives 'UNDERPANTS'.

Can you help me to learn more?

(Other definitions for underpants that I've seen before include "cover and support" , "Intimate clothing" , "Close-fitting garment" , "drawers" , "Shorts" .)

I've seen this clue in The Telegraph.

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