Ha! I knew Berlanti and Kreisberg couldn’t stay away from Darren Criss forever. The producers of the four DC ‘verse shows on The CW have an affinity for casting Glee alumni (Melissa Benoist, Grant Gustin) and Michigan State/Starkid alumni as well (Carlos Valdes, Andy Mientus). Darren is the pinnacle of that trend, fitting both groups.
The Flash and Supergirl, starring Gustin and Benoist, are doing a musical crossover which will air Monday, March 20 and Tuesday, March 21. Most of the crossover will be on The Flash. Supergirl will probably get just enough to explain her presence in Central City, the way she did during the December crossover that incorporated all four Berlantiverse shows.
Winn/Jeremy Jordan will be crossing over with Kara/Melissa Benoist. Dr Stein/Victor Garber and Malcom Merlyn/John Barrowman will also be pulled in from other parts of the Berlantiverse.