Warm-hearted French friends of a Dumas musketeer (6)
I believe the answer is:
aramis
'a dumas musketeer' is the definition.
(I've seen this in another clue)
'warm-hearted french friends' is the wordplay.
'hearted' means to look at the middle letters.
'french friends' becomes 'amis' (I've seen this in another clue).
The middle letters of 'warm' are 'ar'.
'ar'+'amis'='ARAMIS'
'of' is the link.
(Other definitions for aramis that I've seen before include "One of Dumas's Musketeers" , "One of Dumas' three musketeers" , "Fictional musketeer" , "One Musketeer" , "Literary musketeer" .)