The French hard-hearted king? (4)
I believe the answer is:
lear
'king?' is the definition.
(Shakespeare's King Lear)
'the french hard-hearted' is the wordplay.
'the french' becomes 'le' ('the' in French).
'hearted' indicates the central letters.
The middle letters of 'hard' are 'ar'.
'le'+'ar'='LEAR'
(Other definitions for lear that I've seen before include "tragic figure" , "hardly the 7 [NO NONSENSE] type!" , "Playful king and writer of nonsense verse" , "Role at Stratford" , "Tragic Shakespeare king - quite real" .)