Torchwood star Barrowman will play a "pivotal" role known only as the "well-dressed man" on the CW superhero drama, but the show's execs have hinted that the character will be one that comic fans recognise.
"He's a mystery at first," Greg Berlanti told GiveMeMyRemote. "I think people will be really excited when we finally reveal who he is [playing]."
Marc Guggenheim added: "He is incredibly magnetic - he is a remarkable actor and seeing scenes with him is just the biggest thrill. He's phenomenal - what a great addition to the cast."
The second exec also stressed the importance of secrecy with regards to Barrowman's role, adding: "Because of the nature of his character, the whole point of the character is not to talk about him. There's a lot of surprises coming!"
Katie Cassidy (Gossip Girl), Willa Holland (The OC), Paul Blackthorne (The River) and Annie Ilonzeh (Charlie's Angels) will also star in Arrow.
The series premieres on October 10 on The CW in the US. Sky1 will air the series in the UK.
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Watch a preview of Arrow below: