Board Thread:Arrow discussions/@comment-9346948-20181211010912/@comment-3030984-20181211123557

Xandermcc wrote: We'll see hopefully. John's interview means nothing until it is confirmed in an episode. After all, Melissa Benoist said Batwoman was going to be on Earth Thirty Eight and that ended up being wrong.

How could it be confirmed within an episode? Unless he turns to camera and goes "You remember that 90s Flash show I starred in? I'm playing the same guy!", you'll almost certainly not get one.

Constantine's in-universe status was similarly confirmed by Word of God. I agree another source is needed - ideally from the production team or similar - but should not need to rely on an in-universe confirmation.