The French entrance Papal ambassador (6)
I believe the answer is:
'papal ambassador' is the definition.
(I've seen this before)
'the french entrance' is the wordplay.
'the french' becomes 'le' ('the' in French).
'entrance' becomes 'gate' (type of entrance).
(Other definitions for legate that I've seen before include "Late, eg. for the papal representative" , "Official emissary" , "Papal ambassador" , "papal emissary" , "Envoy representing the Pope" .)