With Grant Gustin first appearing as Barry Allen in Arrow, it makes sense for The Flash to return the favor as it's learned that Stephen Amell will appear in the pilot.
Stephen Amell confirmed the news:
In the Flash pilot, Barry comes to me. [It's a] little snippet in the Flash pilot where he and I share a scene together, it's in his pilot, but [filming] it felt like our show because he's coming to Starling City. That, to me, was one of the most rewarding things that I did as an actor because it was essentially the same crew that we used for our pilot, and it was two years later and it was the same director. It was like going back in time. [Flash and Arrow director] David Nutter asked me to be a part of the pilot and I will never say no to David Nutter.
The Flash airs Tuesdays at 8pm ET this Fall on the CW.
After a particle accelerator causes a freak storm, CSI Investigator Barry Allen is struck by lightning and falls into a coma. Months later he awakens with the power of super speed, granting him the ability to move through Central City like an unseen guardian angel. Though initially excited by his newfound powers, Barry is shocked to discover he is not the only "meta-human" who was created in the wake of the accelerator explosion -- and not everyone is using their new powers for good. Barry partners with S.T.A.R. Labs and dedicates his life to protect the innocent. For now, only a few close friends and associates know that Barry is literally the fastest man alive, but it won't be long before the world learns what Barry Allen has become...The Flash.