Lena Headey made pal sign blood pact after Game of Thrones spoiler reveal

Lena Headey tracked a friend down and made her promise never to repeat what she had told her on a drunken night out after revealing how a Game of Thrones season ended.

The actress, who plays terrible Queen Cersei Lannister on the fantasy drama, insists she is usually very good at keeping the show's plots and twists a secret - unless she's had a few drinks on a night out with pals.

"The next day I hunted them (friend) down and made them sign in blood not to say anything," Lena tells Entertainment Tonight, recalling the moment she realised she had dropped a major spoiler.

The actress admits it is frustrating at times when she's constantly asked to reveal all about the show.

"It's part of the success, you know, being consumed with it and what's happening," she explains. "I think it's just frustrating when you do interviews for Game of Thrones and actually can't say anything."

And she's not about to break her habit two months before the final season of the show starts, simply telling anyone who asks, "I think people will be surprised at every turn this season."

Meanwhile, Headey admits that, like her castmates, she has always skipped to the end of each script she receives at the start of each season to make sure her character is still alive.

"Every year, anyone's lying if they say they didn't kind of rush to the end of each script and go, 'Oh, phew!" she laughs.

The final episodes of Game of Thrones will air from mid-April (19).