Joe's double in a movie (4)
I believe the answer is:
gigi
'movie' is the definition.
(I've seen this before)
'joe's double' is the wordplay.
'joe' becomes 'GI' (GI Joe).
'double' says to double the letters.
'gi' duplicated is 'GIGI'.
'in a' is the link.
(Other definitions for gigi that I've seen before include "Lerner and Loewe musical and film" , "1958 film musical from a Colette novel" , "Movie" , "Musical, winner of nine Academy Awards" , "1958 film, winner of 9 Academy Awards" .)