"Game of Thrones" actress Lena Headey may have posted the mother of all spoilers on her official Instagram account.

[Warning: POSSIBLE SPOILERS AHEAD]

Headley, who plays Cersei Lannister in the hit HBO series, posted a photo of a heart made out of stones with the caption, "my stone heart." For those who are unfamiliar with George R.R. Martin's novel it looks like a pretty photograph.

However, those who have read the novels are speculating Headey could be teasing the reintroduction of a major character in the series: Catelyn Stark. Catelyn died at Robb Stark's wedding after a betrayal by Walder Frey.

In the novels, Catelyn claws at her face before her throat is slashed. She is very much dead, until she is resurrected and lets vengeance consume her. She becomes Lady Stoneheart, killing anyone who she believes helped kill her son or anyone who gets in her way.

Headey's photo could just simply be a nice picture or a sly reference for what's to come in the series. "Game of Thrones" fans will have to wait two weeks for the next episode in the series.

In other "Game of Thrones" news, Martin recently visited Conan O'Brien's late night show and explained why it isn't so difficult for him to kill off his characters.

"I killed them years ago in the books," Martin said, referring to the many deaths in the HBO adaptation of the series. "At that time we didn't actually have an actor who playing [Joffrey]. Jack Gleeson, who played Joffrey, was actually the nicest guy in the world."

"I think it's a good thing that I wrote the books before we started making the show," he added. "Because when you make the show and you actually meet the actors, then it's harder to kill them...because Jack will be out of a job then."