Matthew McConaughey has a darker side than people expect, director William Friedkin has revealed.

The Texan actor, who is better known for playing the romantic lead in films like Ghosts Of Girlfriends Past, Fool's Gold and Failure To Launch, stars as a charming hitman in William's thriller Killer Joe alongside Gina Gershon and Emile Hirsch.

"Well he isn't the guy in these romantic comedies. He's more like Killer Joe," said the filmmaker.

"The reason he did How To Lose A Guy In Ten Days and about 20 other films like it was because he's a very good looking guy and in Hollywood if you're a good looking woman or guy you get cast that way. They don't want you to act. They want you to just show up and be good looking."

He added: "Julia Roberts doesn't have to act but she's capable of acting if she gets a decent role. That's true of McConaughey."

William also defended a controversial scene involving fried chicken.

"I had no reservations. Neither did the actors, Matthew or Gina Gershon. She understood that this was an act of vengeance and it's patently absurd but I understand it puts people off. It's a very challenging scene," he added.

Killer Joe is in cinemas now.