Add fanciful details to glowing piece about French King and daughter (9)
I believe the answer is:
embroider
'add fanciful details to' is the definition.
'glowing piece about french king and daughter' is the wordplay.
'glowing piece' becomes 'ember'.
'about' is an insertion indicator.
'french king' becomes 'roi' (I've seen this before).
'and' means one lot of letters go next to another.
'daughter' becomes 'd'.
'roi'+'d'='roid'
'ember' placed around 'roid' is 'EMBROIDER'.
(Other definitions for embroider that I've seen before include "Sew decoration onto" , "Ornament with needlework" , "Sew; embellish" , "Elaborate" , "Elaborately sew" .)