Speaking to TV line Grant Gustin, the Flash from The CW revealed 

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Mahender | 17 Apr 2023

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there you go. Or maybe they can play with some ideas of when he's in the Speed Force 

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seeing The CW flash over there, and the meeting. So maybe it's not new footage that he shot. Maybe it's old footage

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We don't know. He's using some tricky words here, in my opinion. I think it would be really disrespectful if you don't

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put Grant Gustin in the film because he literally carried those boots for the Flash for about a decade while the film

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was struggling to get off the ground and really made the Flash. Something that WB realized they could literally

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turn into a film, was that they announced the film the week after the show premiered because of the huge success.

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And everybody going, wow, I can't believe this isn't a film. So a lot of people pointed out that was disrespectful

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so you better pay back the actor that literally paved the way for Ezra to be able to do this film. I think it's only right if he's not in it