When it comes to DC Comics, events from the 1988 one-shot graphic novel The Killing Joke have not really been a part of that universe's continuity.

Perhaps one of the most controversial parts of that story was the crippling of Barbara Gordon by the Joker, who was doing his best to torment her father into going crazy. Many argued that the story didn't honor who and what Barbara as Batgirl was, but it did set her up to later become bound to a wheelchair, taking on the mantle of Oracle.

The New 52, though, decided to completely do away with that persona: Barbara underwent an experimental surgery that healed her and she became Batgirl again. As the new Batgirl comic progressed, though, the incident from The Killing Joke faded away, and eventually, DC believed that it didn't even play into her story, that it wasn't part of the overall continuity.

That all changes in Batgirl and the Birds of Prey: Rebirth #1. In Batgirl's Rebirth issue, the what happened to Barbara in The Killing Joke isn't just mentioned, but also confirmed as something that happened to her character. The book opens with Batgirl musing about time and how it doesn't heal all wounds, and leads into her recapping her origin.

However, that origin story includes an important element: a panel featuring Joker in his Hawaiian shirt from The Killing Joke, camera around his neck, as Barbara remembers what he did to her.

This is perhaps the first real confirmation that The Killing Joke exists within DC Comics continuity, and could even play into the future of the new Rebirth titles. It also shouldn't come as a big surprise to DC Comics fans, because Batman: The Killing Joke becomes a movie this year with a lot of hype surrounding it: Fathom Events recently added an extra day for theatrical screenings of the film because of high demand.

So, what does this mean? It means that today's Batgirl is the one we saw in The Killing Joke. She is also the Barbara Gordon that survived that attack and went on to become Oracle. The new book also confirmed the surgery that healed her, while it brings her back together with Black Canary as the two go in search of another who now claims the Oracle title.

It's an interesting development for a graphic novel that was never meant to become part of the DC universe continuity.