Hot on the news that actress Eliza Dushku will lend her voice to the upcoming motion comic series for Torchwood: Miracle Day, producer Russell T. Davies has revealed a twist for the upcoming season.

If you don’t want to know what it is, please stop reading now. It’s a SPOILER….

Saying that he wants to shake up things a bit for the characters in series four, Davies revealed that the upcoming season will find Captain Jack Harkness becoming mortal again.

“The greatest thing you can do is offer a new look into the character. It’s not fundamentally altering the character, it’s fundamentally altering the rules [while] the character stays the same,” Davies tells AOL TV.

He hinted that Captain Jack’s new condition will be linked to the premise of Miracle Day, which sees the entire populace of Earth unable to die.

“Everyone else is immortal, [and] he’s mortal,” he says. “It’s the biggest switch in the show, which we did in order to give us new insights into Jack.”

Davies added that he “couldn’t possibly say” if Jack will be killed off in a future episode.

“The stakes are that high,” he admitted. “And it’s very hard to prove he’s mortal without killing him, so that’s going to be interesting.”