So, I recently decided to learn Blender and to do that, I started a small mash up project.

Everything was going along fine, until, to save time, I deleted half of the face mesh, worked on it, duplicated it and mirrored the duplicate. Now as long as I export the two halves as two separate emds it works fine ingame, but every time I join them and export it as one mesh, I get the following:

Ingame:                                                                                                                                Blender:

(ignore the textures, I haven't begun working on those...)

Has anyone encountered a similar problem or just knows where I ****ed up?

Thanks in advance.