Conversation so far:
what episode of supergirl is the flash crossover
Duet is the seventeenth episode of the third season of The CW television series The Flash and features a musical crossover with Supergirl.
who wrote the flash episode duet
The Flash episode Duet was written by Aaron Helbing and Todd Helbing from a story by Greg Berlanti and Andrew Kreisberg.
can you tell me who directed the flash episode duet
The Flash episode Duet was directed by Dermott Daniel Downs.

Question: when was the episode filmed
Self-contained rewrite: when was the flash episode duet filmed