'The Flash': Extended Trailer Features An 'Arrow' Crossover

...But will they cross over with every other CW show?

You knew it was coming, but "Arrow" spin-off "The Flash" will get a crossover as soon as the first episode. The extended trailer for the pilot has Stephen Amell's Oliver Queen offering Grant Gustin's Barry Allen a key piece of advice that Barry first gave Ollie back on "Arrow."

We'll have plenty more on both shows out of the CW Upfronts later in the day.