The CW's massive Arrowverse crossover Crisis on Infinite Earths came with no shortage of shocks—Oliver Queen is dead! All the CW shows are on the same Earth now! Swamp Thing was a show!—but none more genuinely surprising than Ezra Miller's cameo as the DCEU's big-screen Barry Allen. Once the bewilderment wore off, the big question became how in the hell did Team Arrow smuggle Miller into Vancouver without that info leaking? And how did they get permission in the first place?

Turns out, that answer might be the most surprising part of all. In an interview with Variety, Arrowverse architect Marc Guggenheim revealed that Miller's cameo was actually Warner Bros.' idea, suggested way after production had already concluded.

We were series wrapped on “Arrow,” and we were wrapped on the whole crossover. We were in post and some episodes were locked, and some were soft-locked. I got a phone call from [Warner Bros. boss] Peter Roth saying, “I know you’re locked, but can you put Ezra into the crossover?” And I said, “Yes.” And he said, “How, you’re series wrapped? And you’re wrapped on the crossover.” And I said, “Yeah, I know, but if you’re telling me Ezra Miller can be in the crossover, I can make it happen.” I called Eric Wallace who who is the showrunner of “Flash,” and he called up Grant Gustin — because the one thing that was our only concern was the thought we didn’t want to do it unless Grant was 100 percent on-board with it. And he was. He was incredibly enthusiastic and on-board with it. And then we got on the phone with Ezra Miller and told him the scene I had written and he was completely into it. And we just went. We put together a unit of the “Flash” crew on the “Flash” set [since “Arrow’s” team, which had produced the rest of the hour, was gone]. And much to our surprise, no one noticed Ezra Miller was in Vancouver and no one leaked it from the crew, which we appreciate. So we were able to keep it a surprise.

That is...super strange, no? Warner Bros. wants to get Miller into an Arrowverse crossover, but it's also suffered setback after setback (after setback) trying to do get his standalone Flash movie off the ground, most of them over creative differences. And the studio has finally settled on a creative team and premiere date for that film—Andy Muschietti, July 1 2022—so it's not like this cameo was done to gauge interest.

Either way, we got one heckuva moment out of it, so let's not suffocate a good thing to death. That's what Ezra's Flash costume design is for. If you want even more Crisis on Infinite Earths, check out the video of Miller's Barry Allen meeting Grant Gustin's Flash.