Surprise! Katie Cassidy's coming back to 'Arrow' as a series regular in Season 6

Well, this is unexpected.

Katie Cassidy will be returning to Arrow as a series regular in Season 6 -- despite the fact that her character, Laurel Lance (aka Black Canary), was killed off in Season 4.

In the world of superhero shows, anything is possible -- and Laurel's sister, Sara (Caity Lotz) has already proven that you can't keep a good vigilante down, having died and been resurrected on Arrow before moving over to spinoff series DC's Legends of Tomorrow.

But Cassidy won't be reviving the Laurel Lance that fans knew and loved for the first four seasons of Arrow -- she'll be playing the Earth-2 doppelgänger version of Laurel, aka Black Siren, a metahuman criminal who was brought over to Earth-1 by the villainous speedster known as Zoom in The Flash Season 2.

After Zoom's defeat, Arrow villain Prometheus tried to enlist Black Siren in his vendetta against Oliver Queen (Stephen Amell), forcing her to imitate Earth-1 Laurel to try and manipulate him. Black Siren was eventually captured and taken into ARGUS custody, but her story clearly isn't over yet -- Cassidy will appear in the final two episodes of Arrow Season 5, and return as a series regular for Season 6.

"One of the things that most excites us about Arrow is that we go where the story takes us," said Arrow showrunner Marc Guggenheim in a statement. "Last year, the story took us to the tragic death of Laurel Lance. This year, our midseason finale reintroduced us to Laurel’s doppelgänger, Black Siren. We were so taken by Katie’s fearless interpretation of this character that we knew her story was not yet finished. We couldn’t be more thrilled to welcome Katie back to Arrow as Black Siren, though as her appearances on Arrow and DC’s Legends of Tomorrow this season show, she never really left the family."