Eclipse, the third film in the Twilight Saga, will be the darkest movie yet, screenwriter Melissa Rosenberg has revealed.

Rosenberg said a combination of the movie's storyline and director David Slade vision for the plot were behind Eclipse's dark turn.

"David has a darker sensibility, so it clicks," Rosenberg told E! Online.

"The story has a slightly darker tone. I mean, it goes into a full-out battle, so it is darker in the nature of what it is. David was the perfect director for it."

But despite the change in tone, Rosenberg insisted that fans would still be able to relate to the story, which has been adapted from Stephenie Meyer's novel.

Robert Pattinson on the set of Eclipse.

"They have the continuity of having the same writers and same actors, but the directors put their own stamp on it,” she said.

"They'll be similar, but very different."

Robert Pattinson, Kristen Stewart and the rest of the Twilight cast are currently shooting Eclipse in Vancouver, Canada.

The film is released next summer.

Twilight