Gene or Grace (5)
I believe the answer is:
kelly
This clue is a double definition.
'gene' is the first definition.
(I know that gene can be written as Kelly)
'grace' is the second definition.
(actress Grace Kelly)
(Other definitions for kelly that I've seen before include "Ned ---, Aus. outlaw" , "Gene --; Grace --" , "Grace --, US actress who married a prince" , "- - Sotherton, athlete" , "- - Holmes, Olympic athlete" .)