The recently released synopsis for The Flash’s ‘Duet’ explained the setup fans will see when the musical crossover airs in two weeks.
The Flash Tuesday March 7 with ‘The Wrath of Savitar’ at 8pm on The CW.
Supergirl continues Monday, March 20 with ‘Star-Crossed’ at 8pm on The CW.
Based on the vintage sepia tones, clothing, and settings of the scenes from the ‘Duet’ promo, these glimpses are undoubtedly from that alternate reality – which additionally explains those 1940s set photos for The Flash.