Grant Gustin took to his Instagram account to shared a first look set photo as the episode is filming.
"Those two emblems look pretty good together..." Gustin offered.
Gustin also posted a pic of the director's chairs used for the episode, adding: "Hey Flash producers... I've already got a fancier chair on Supergirl than I've got on Flash. Just saying..."
You can also check out the Supergirl Easter Egg featured in last night's episode of The Flash.
"Supergirl" airs Mondays on CBS at 8pm ET; "The Flash" airs Tuesdays on The CW at 8pm ET.