"Arrow" star Stephen Amell may have crossed fandom streams, and ignited the dreams of millions, with a single photo caption.

The actor was a guest Saturday in Los Angeles at Entertainment Weekly's PopFest, where he joined "Supernatural" stars Jensen Ackles and Jared Padalecki, "The Flash's" Grant Gustin, "Supergirl's" Melissa Benoist and "Legends of Tomorrow's" Caity Lotz for a squee-inducing group photo.

The image would've been enough to please devotees of the five CW dramas, but then Amell had to add a caption on Instagram: "This is the crossover we need." (That sound you hear is the collective fan base of the shows screaming, "YES!")

This is the crossover we need.

A photo posted by Stephen Amell (@stephenamell) on

The upcoming three-part crossover bringing together "Arrow," "The Flash," "DC's Legends of Tomorrow" and "Supergirl" is ambitious enough, so it's probably too much to expect "Supernatural" might be added to the mix, say, next year. However, perhaps we shouldn't discount the possibility entirely.

After all, Oliver Queen called in John Constantine on "Arrow" to help restore the soul of Sara Lance. And "Supernatural," now in its 12th season, is nothing if not flexible, willing to embrace humor, time travel and self-awareness. So why couldn't the Winchester brothers, pay a visit to the Arrowverse, perhaps through the intervention of a trickster or an angel -- or maybe Barry Allen?

All right, maybe that's too much to hope for.

Here's a shot of @jaredpadalecki smacking my ass and me not hating it.

A photo posted by Grant Gustin (@grantgust) on

(via EW)