'Game of Thrones' Star Lena Headey -- Queen Cersei Files for Divorce

"Game of Thrones" star Lena Headey -- who plays the cruel Queen Cersei Lannister on the show -- has filed for divorce from her real-life husband ... TMZ has learned ... and no, it's not her brother.

Lena filed the docs last week in L.A. County Superior Court against husband Peter Loughran, citing "irreconcilable differences."

The couple was married in May 2007. They have one son, born in March 2010.

As far as we know ... her son is NOT an intolerable little twit bent on world domination.