The cast of The CW's hit show "Arrow" is about to get even bigger with a few members of "Flash" joining the show. Executive producer Marc Guggenheim recently discussed the expanding cast, while revealing some spoilers.

It seems that actress Danielle Panabaker and actor Carlos Valdes will star in at least one episode of "Arrow." The two actors had roles in the first episode of "Flash." Mac Guggenheim spoke to TV Guide about when Panabaker and Valdes will be showing up on "Arrow."

The two "make an important appearance in Episode 19 of Arrow," the executive producer said.

Guggenheim went on to say that the additional cast members were necessary, and came about naturally in the plotline.

"This was something that really came about because obviously Barry is in a coma at the end of Episode 9," he said.

The executive producer went on to elaborate on why the two characters are joining the show.

"The idea of bringing in those characters really, really appealed to us because it allowed us to honor our original intention [of] doing something Flash-related around Episode 19 or 20 without having comatose Barry and basically paying Grant Gustin a lot of money to sit around with his eyes closed just unconscious the whole episode... This episode is really cool. It allows us to further flesh out the 'Flash' universe in 'Arrow,'" Guggenheim said.

Catch "Arrow" on the CW Wednesday nights at 8/7c.