Cassidy will in fact return to the CW series in the final two episodes of this season, playing dearly departed Laurel Lance’s Earth-Two doppelgänger, the metahuman Black Siren, then continue in the same role starting this fall.
In announcing Cassidy’s new deal, Arrow co-showrunner Marc Guggenheim said in a statement, “One of the things that most excites us about Arrow is that we go where the story takes us. 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,” he added, “though as her appearances on Arrow and DC’s Legends of Tomorrow this season show, she never really left the family.”
As announced last month via Twitter, Cassidy will appear in Legends‘ Season 2 finale (airing Tuesday, April 4), but as Laurel.
Cassidy was an original Arrow cast member and stuck with the series until the final stretch of Season 4, when Damien Darhk fatally stabbed Black Canary with one of Oliver’s arrows. She has made six #DCTV appearances since then, though, either in flashbacks, as part of an alternate reality or as Black Siren.