Alex (Decoys)

Alex is a character in the 2004 science-fiction/horror film Decoys. Appearing as the girlfriend of Luke, the protagonist, for most of the film, she is revealed to be an alien in the last few minutes.

History
Initially, Alex is seen as Luke's girlfriend, albeit one that's often neglected. Luke is seen to constantly be interested in other women, and during an escapade in which he attempts to spy on two naked blondes, he discovers them sprouting tentacles. Eventually Luke learns that alien women have come to earth seeking human mates, whom they copulate with to produce alien children. Unfortunately for the men, the process involves the aliens sicking tentacles down the humans' throats and planting their embryos, which generates extreme cold that ends up killing the humans.

Luke ends up hunting after these alien girls, and Alex helps him. Luke himself gets into several close calls as he tries to expose or kill the aliens, nearly getting impregnated himself. Eventually, with the help of a former cop girlfriend, Luke manages to kill the last alien, and believes himself successful. Alex congratulates him, and takes him to her bedroom, where she seduces him.

Luke realizes Alex has been there for him this whole time, and professes his love for her, which Alex returns in kind.

Reveal
Alex continues to seduce Luke, kissing him and allowing him to undress her. A shot reveals that Alex has no navel, suggesting she is one of the aliens. Alex smirks as she becomes aroused, then turns and takes Luke to the bed. Luke lays Alex down on the bed, but Alex wraps her legs around him and pulls him down, then mounts him. Luke, surprised, gets up, but Alex wraps her arms around him, trapping him. She brings his face close to her, and thanks him for getting rid of the other aliens, and that she can now have her way with him. She then pushes him down and straddles him menacingly. Flashbacks reveal Alex was the one that was sabotaging Luke's attempts to reveal the aliens.