Warning: Spoilers ahead not just from "Game of Thrones" but from the "A Song of Ice and Fire" book series.

Valar Morghulis, all men must die. But what about queens? "Game of Thrones" now has Cersei Lannister on the Iron Throne in King's Landing, but even actress Lena Headey said she doesn't expect Queen Cersei to last long; when Cersei is killed, Headey said she just wants it to be "by the right person." To her, that "right" person, at least by the end of Season 6, was Arya Stark or Cersei's younger brother Tyrion Lannister.

Fans, however, have a different theory, based on George R.R. Martin's books. They think Cersei will be killed by her other younger brother, her twin brother, Jaime Lannister.

You know who's not into that theory? Jaime Lannister actor .

The Jaime kills Cersei theory comes from Maggy the Frog's prophecy for Cersei. Maggy foretold that "Queen you shall be... until there comes another, younger and more beautiful, to cast you down and take all that you hold dear." Cersei took that to mean Margaery Tyrell, but fans always suspected was Daenerys Targaryen. Maggy also told Cersei her death would come from the hands of "the valonqar," which is High Valyrian for "little brother": "...And when your tears have drowned you, the valonqar shall wrap his hands about your pale white throat and choke the life from you."

Cersei thought that meant Tyrion, but fans think it's Jaime, with that dark Season 6 finale look between them as a big clue:

The Huffington Post asked Coster-Waldau about the theory that Jaime could kill Cersei. It's not like the actor could confirm it, so it shouldn't be a surprise that he said this:

"It's a theory ... but it has a beautiful, romantic, tragic thing [to it]. It's probably too obvious."

However, he added that he ultimately has "no idea" at this point how it turns out. If true, it suggests Cersei at least lives through Season 7 into the final Season 8.

But it seems like Tyrion killing Cersei is what would be too obvious. Jaime is the one fans won't expect, unless they've been following the hints in the books and -- more subtly at this point -- on screen.

"Game of Thrones" Season 7 arrives on HBO some time this summer.

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