Back in October, Marvel Comics writer Jason Aaron took a pretty bold new step as the writer of Thor. He made the original, blonde Asgardian beefcake Thor suddenly unworthy to wield the mighty hammer Mjolnir, and gave both the hammer and the name of Thor to a woman. Many fans were intrigued, some were pissed, but everyone took notice.

At the time, Aaron spoke at length to Playboy about how he wasn’t trying to craft an impermanent publicity stunt to grab sales, and about how he definitely had long term plans for the new Thor. What he didn’t reveal was who she really is, and the mystery has spawned fan theories that it’s everyone from Lady Sif to Thor’s relatively new Asgardian sister Angela (who’s only been in the Marvel Universe since 2013). Tomorrow, in the pages of Thor #8, the question will finally be answered, but thanks to a new interview Aaron gave to Vulture, we already know who’s wielding the hammer. So, if you don’t want to know until you’ve read the comic, look away now, because it’s SPOILER TIME.

The female Thor who’s been wielding Mjolnir since October turned out to be none other than Jane Foster, a character who’s been a presence in Thor comics since 1962, and was played by Natalie Portman in both Thor films so far. In the current comics, Foster is suffering from breast cancer, and though she becomes a mighty Asgardian warrior when she picks up Mjolnir, her illness gets worse when she becomes herself again. As if that weren’t enough to deal with, she’ll also be seen in the upcoming Secret Wars series Thors, battling evil alongside other incarnations of the God of Thunder.

Here’s what Aaron had to say about why he chose Jane to wield the hammer, and why she was always the only choice.

“Jane’s been a part of Thor’s universe going back almost to the very beginning. She was the initial love interest for Donald Blake, who was Thor’s alter-ego [in early Thor stories]. She was the nurse to his doctor. She’s grown and changed and evolved a lot over the years, become a doctor in her own right. So this to me is not just the next step for her character, but really the next evolution of the core promise that has always been at the heart of Thor’s mythology.

"You go back to those very first issues [from the 1960s], and they’re about this disabled doctor, Donald Blake, finding a strange hammer, and when he picks it up, it transforms him into the mighty Thor. That promise of transformation has always been a part of that hammer. Even though we’ve changed the person who’s holding the hammer, it’s very much a Thor story, a story that begins the next step for that promise of transformation.”

So, now the secret is out, and Aaron can begin to tell a more transformative story to readers who are in on the mystery. To find out more, pick up Thor #8 in comics shops or digitally tomorrow.