TVGuide have earlier today broke the news that Arrow and The Flash will be crossing over in a massive two-hour event later this year!

So far there's been really no information as to how it'll happen or anything, though it is said to be both series' eighth episodes, but Felicity Smoak has been confirmed to appear in The Flash's fourth episode, "Going Rogue", so that should be a heap of fun to watch until it builds up to the momentous crossover event, so stay tuned!