Faithful in Belgian city (5)
I believe the answer is:
liege
I believe this clue is a double definition.
'faithful' is the first definition.
(I've seen this before)
'belgian city' is the second definition.
(I've seen this in another clue)
'in' acts as a link.
(Other definitions for liege that I've seen before include "Old sovereign" , "Owing feudal allegiance" , "Belgian city or ancient lord" , "Large Belgian city" , "European province" .)