Enigmatic, popular former wife, flexible about clubs (12)
I believe the answer is:
inexplicable
'enigmatic' is the definition.
(thesaurus)
'popular former wife flexible about clubs' is the wordplay.
'popular' becomes 'in'.
'former wife' becomes 'ex'.
'flexible' becomes 'pliable' ('pliable' can be similar in meaning to 'flexible'**).
'about' is an insertion indicator.
'clubs' becomes 'c' (abbreviation used in card games such as bridge).
'pliable' placed around 'c' is 'plicable'.
'in'+'ex'+'plicable'='INEXPLICABLE'
(Another definition for inexplicable that I've seen is " Impossible to explain".)