Sean Penn & Charlize Theron -- Reunited and It Feels So Awkward (PHOTO)

Sean Penn and Charlize Theron were back together Wednesday after they were forced to reunite in South Africa for re-shoots on the set of their movie ... six weeks after they ended their engagement.

To make matters worse ... Penn's the director of "The Last Face" and Theron's the star ... so he's her boss. Not awkward in the slightest.

Theron and Penn broke things off back in June after getting engaged in December 2014.