The Achilles X is a good call but usually has stronger tail markings, darker body colours, and orange at the base of dorsal & anal fins and edging the socket.
A number of species have been known to hybridise, but they don't do it regularly (or at least it's not recorded as a regular occurrence). The Achilles x Whitecheek has been recorded in at least four different places in the Pacific (I saw them in Tokelau four years ago).
