Could The Dark Knight's son be coming to Arrow? I don't know how certain we can be, but TV Line has a pretty interesting take on the idea:
The show’s Season 3 finale will introduce a major, formidable, fierce new foe for Oliver, and his reign of terror will continue well into Season 4. The mysterious character is being referred to internally as “Damian Dark,” which got [us] pulling up and skimming the Wiki page of one Damian Wayne.
Get it? Damian Wayne. Son of the Dark Knight. They’d probably have to tweak the Bruce Wayne connection, but it’s a plausible theory, no?
Who do you think 'Damian Dark' will be?