Lena Headey talks about Cersei Lannister's arc in GOT Season 5

The finale was huge for your character. We see her finally confess to Tywin that she’s in love with her brother, Jaime, and that his legacy is screwed.

I’ve known Charles [Dance] for a long, long time, and he’s pretty formidable. He’s a pussycat off-screen, but he’s ferocious as Tywin. There’s always that strange feeling when you know someone and you’ve spent a lot of time together, and a part of you is thinking, “Shit, this is it. It’s the last time I’m going to get to look in your eyes and do what we do.” It’s kind of weird. But I love that Cersei has that moment of, “Oh, fuck it. My kid’s fucking dead and you’re a shit, so I’m going to tell you how it is.”

Cersei, for all her ruthless scheming, has gotten a really raw deal. She’s constantly diminished by Tywin and treated like a second-class citizen.

He is, without a doubt, the shittest Dad in the world. All she’s wanted to do is sit with him and have him tell her she’s doing great, and he loves her, but she’s given up on that. As a child, you never stop wanting to be validated by your parents—especially with a daughter to a father—and that’s why she has problems with her brothers, because she thinks, “If I were a guy, this would be easier.” But she has a lot to contend with, Cersei.

Cersei’s relationship with Jaime has gone through so many twists and turns. When he first returns with his golden hand, she views him as slightly pathetic. He’s no longer the “Kingslayer” she knew and loved but deformed. Then, in the finale, she professes her love for him.

She comes back and she’s a bit like, “Ugh… I don’t know,” and then when he shows interest in Tyrion, she begins to feel that Jaime recognizes something in her that he doesn’t necessarily want to fight for anymore. He says, “Why have the Gods made me love a hateful woman” over the body of their dead son. He’s never said anything like that to her before, and he also stands up to her on Sansa. She’s a kid, Cersei. She doesn’t want the toy unless somebody else wants it, and I think that’s how she is with Jaime. So right now she’s manipulating him, and I don’t know how long that’s going to last but I think he’s had a big change of self.

You’re great at playing this pretty sinister character. How do you get into Cersei mode? Do you have a ritual for transitioning to the dark side?
[Laughs] No. I don’t think she’s particularly dark! I think she’s a survivor and holds onto a reality that she’s created, and it’s very small because it’s full of denial for her, so next season it all starts to fall apart. But the process of going in in the morning and getting the corsets and wigs done and walking onto sets like that really helps, and being an actor and having belief in what you do is the biggest commitment I have in my life besides being a parent.
You mentioned that “it all starts to fall apart” for Cersei next season, but she’s also in a position of great power now that Tywin’s gone. As Tommen’s mother/adviser, she’s essentially second to the throne.

Also she’s lost Joffrey and that was a prophecy when she was small and her ability to live in fantasy is getting smaller. She’s also fearful because Margaery is getting very close to Tommen and she really doesn’t like her very much. I don’t know how they’re going to write her reaction to Tywin’s death, but I’m sure there’s going to be some sort of celebration for her in it. But Tywin’s also given her the knowledge that the Lannisters are pretty much broke, so I think she’s overwhelmed with it all.

In the books, Cersei gets very down in the dumps, starts putting on weight, and hits the bottle hard.

I love that! I think the more broken the better. Cersei’s built where you meet her as this woman who seems to have it all under control—her head’s very nice and she’s well-dressed—and underneath it’s a whirling mess. So we really get to see what’s underneath that façade as the seasons go on, and I think next season is going to be particularly brutal for her.

You said you don’t think Cersei’s particularly dark, but her hatred of Tyrion is pretty evil. When the Red Viper describes how she treated baby Tyrion…thank God they didn’t show that in flashback.

There’s time! There’s time! [Laughs]

Oh goodness, I hope not. But she hates Tyrion so much for “killing” their mother that it’s really colored her outlook on things. Do you think she even believes he poisoned Joffrey?

I think she’s made herself believe it. Almost since being born, she’s wanted to destroy Tyrion because she blames him for taking away the one person who would have made her life better had she lived, which is her mother. She holds Tyrion responsible for all the shitty things in life and when Joffrey dies it’s painful for her, so her grief is all directed at Tyrion and turns into burning hatred. She just wants to fucking destroy him any way possible.

Full interview at SOURCE