WARNING: The following contains major spoilers for "Crisis on Infinite Earths," the latest Arrowverse crossover.
The CW's "Crisis on Infinite Earths" saved its most stunning cameo for "Part 4." When Oliver Queen's Spectre sent The Flash into the Speed Force, the Scarlet Speedster came face to face with his doppelganger -- and not just any doppelganger. He ran right into Ezra Miller's version of the character, as he appeared in Warner Bros.' Justice League.
The most surprising part of this cameo is the fact that the network was able to keep it under wraps until the time of airing. However, that's not the only reason it was so shocking. After all, Warner Bros. has a history of preventing certain DC characters from appearing on the Arrowverse if they're involved in the DC Extended Universe.
Take the Suicide Squad, for instance. The team made its Arrow debut in 2014 for Season 2's 16th episode, appropriately titled "Suicide Squad." It assembled well-known DC villains like Deadshot and Bronze Tiger, and even ended with a tease for Harley Quinn, an appearance that never materialized. As Warner Bros. geared up for the Suicide Squad film, which arrived in August 2016 to mixed reviews, several of those characters were killed off on the show, including Deadshot in a 2015 episode of Season 3, and Amanda Waller in a 2016 episode of Season 4.
Then there's the matter of Deathstroke. His Arrowverse history has been even more complex, with Warner Bros. pulling the character in early 2016 and late 2017. "The character of Slade Wilson is currently tied up in another DC project," then-showrunner Marc Guggenheim told a fan in February 2016.
In December 2017, Guggenheim told a similar story. "For a time, [DC] was saying 'you can't use Deathstroke,' and then that changed and we were able to have Slade Wilson back on the show... Now we're back to 'you can't use him'... They're working on the feature film version." This is likely in reference to his post-credits appearance in 2017's Justice League; the character, as played by Joe Manganiello, was also due to get his own film, although that never came to fruition.
Warner Bros. has kept mum on the issue, although many speculate the studio believes audiences would become confused if too many versions of these characters appeared across different mediums. Nevertheless, the tide began to shift in recent years. Deathstroke recently appeared in Titans Season 2, with Esai Morales filling the mercenary's boots. Although Manu Bennett's Arrowverse version of the character hasn't appeared since Season 6, the antihero inspired a gang of followers led by Slade Wilson's son, Grant, in seasons 7 and 8.
With The Flash, Warner Bros. has had a bit of a tough time. The CW's Flash premiered on Oct. 7, 2014 -- and that's almost a year after the Barry Allen character debuted in Arrow Season 2, on Dec. 4, 2013. Warner Bros.' The Flash movie was announced on Oct. 15, 2014, just days after The Flash's CW premiere. Since then, The CW's The Flash has enjoyed moderate success by the network's standards, while Warner Bros.' The Flash was delayed by four years and cycled through a number of writers and directors. This set the fans of Grant Gustin's Flash and Miller's Flash against one another, with Gustin eventually telling his followers to tone down their criticism of Miller, despite a perceived jab by Gustin.
Although The CW's Flash has spent years exploring the DC multiverse, the chances of him running into Miller's Scarlet Speedster seemed like a long-shot at best. Nevertheless, "Crisis on Infinite Earths" managed to pull off the impossible: a Miller appearance in the Arrowverse. What's more, as these behind-the-scenes photos from Gustin go to show, the Flashes of both Earths couldn't be happier about it.
"Crisis on Infinite Earths," the latest five-show crossover between all the Arrowverse series, will soon be available on The CW's streaming service in its entirety.