Lena Headey made her friend ''sign in blood'' that they would not reveal 'Game of Thrones' spoilers.

The plot of the television series is a closely guarded secret but the actress - who plays Queen Cersei Lannister in the fantasy show - admits she told her pal something she shouldn't have when she was drunk.

However, Lena was keen not to let it get out of hand and she ''hunted'' her friend down the next day and made her promise to never reveal what she had told her on the night out.

She said: ''The next day I hunted them [her friend] down and made them sign in blood not to say anything.''

And Lena admits it can be frustrating when she is asked for spoilers all the time.

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

Meanwhile, Lena previously admitted the ending of 'Game of Thrones' made her feel ''emotional''.

She shared: ''I knew that David [Benioff] and Dan [Weiss], our creators, were doing speeches and giving everybody these drawings of the storyboards. And I suddenly got really emotional at the end and tried to head down the stairs. They all rushed up and trapped me. And then they gave the speech, and it was really moving.''

Lena also confessed the cast are always keen to discover how the story will evolve.

She shared: ''They usually give us all of [the scripts], and if anyone says they don't flip to the end, they're lying.''