How "Elseworlds" Part 1 Pays Homage to 'Smallville'

Tonight on a special episode of The Flash, the multiverse-spanning "Elseworlds" crossover kicked off -- and besides Arrow, The Flash, and Supergirl, fans got a glimpse of another CW show.

No, not DC's Legends of Tomorrow and not even Black Lightning. Smallville.

When The Flash (Stephen Amell) and Green Arrow (Grant Gustin) travel to Earth-38 to see whether Supergirl (Melissa Benoist) would realize that they have switched places, they find her visiting with her cousin Clark Kent (Tyler Hoechlin) and Lois Lane (Elizabeth Tulloch). The set, as it happens, is the farm from Smallville -- a location that was instantly recognizable to longtime viewers when actors shared some behind-the-scenes photos during production on the crossover.

In case that (and the glimpse of Earth-90's suspiciously Smallville-inspired Green Arrow in the opening scene) was not enough, the establishing music played when approaching the Kent farm was the theme from Smallville.

When Superman was first slated to come to Supergirl, some fans petitioned to have it be Tom Welling, who played Clark Kent from 2001 until 2011. It did not pan out, although the series has previously made reference to Chloe Sullivan, a supporting character created for Smallville.

It remains a safe bet that Smallville and Supergirl take place on different Earths within the multiverse, if only because Supergirl's backstory on the TV show does not fully match up with the version from Smallville. The theme (and the rest) are likely there as Easter eggs to help fans have more fun with the crossover, rather than any kind of "clue" to be decoded.

"When Greg Berlanti first talked to me about why he wanted to do crossovers, it was because it's for the fans," Arrow star Amell said during a Facebook live during the production of the crossover. "It's so people can watch characters and scenarios that combine their favorite things on TV or introduce them to new things on TV. But you also get this license to do things that we could never do in the vacuum — especially on Arrow — that we can never do in the vacuum of just our show."

"It's awesome," Hoechlin said of Lois being involved with the crossover earlier this year. "It's really exciting to have a lot of these new characters popping into this one. The crossover has always been a huge event, but it seems like there's a lot of new characters coming into it for the first time this time, so it should be a lot of fun."

The "Elseworlds" crossover will begin on Sunday, December 9th with The Flash at 8/7c, followed by Arrow on December 10th at 8/7c, and Supergirl on December 11th at 8/7c.