Helena Bonham Carter admits 'Dark Shadows' is going to be "impossible to sell".

The 'King's Speech' star plays the role of a therapist with a drinking problem in the movie - which also stars Johnny Depp and Michelle Pfeiffer - directed by long-term partner Tim Burton, but she does not think it will be an easy film to market.

She told Deadline.com: "My character's an alcoholic psychiatrist, so I hadn't played that before. And she's got a secret. They all have secrets. It's all about people who have secrets."

"It's very original and it's kind of uncategorisable. It's going to be impossible to sell, frankly, because it's a soap opera, but it's very, very subtle. I don't know. We'll see. It's a ghost story, but then it's an unhappy vampire story."

Chloe Moretz - who also has a role in the movie - previously said she had a "great" time while working on the eccentric movie.

She said: "I play Carolyn, Michelle Pfeiffer's daughter. It's great, it's been amazing. We've been shooting for two months now, it's going really well."