When a person completely and suddenly, and often shockingly, goes from good to evil. The term came from
professional wrestling to refer when a face (
good guy) turned his back on the fans and became a
bad guy (heel).
Anna: Kiss me, only an act of true love can
save me.
*
HEEL TURN*
Hans: True love? I just wanted to marry into your family and steal the throne! Now I'll leave you to die.