The actor previously played Lenny Luthor in 'Superman IV.'
Barry Allen and Oliver Queen are trading places in the epic, multi-show event.
The actor also teased The CW's upcoming crossover event with 'The Flash' and 'Arrow.'
ET sat down with Brook in studio on Thursday. 'Supergirl' is on every Sunday at 8/7 central on the CW.
The new series regular also dished on acting alongside Chyler Leigh and 'Supergirl' newcomer Nicole Maines.
The CW's superhero drama is dealing with a "divided nation" as tensions rise regarding the Earth's alien population.
The 21-year-old transgender actress and activist talks to ET about playing Nia Nal, aka Dreamer.
The CW's superhero drama is bringing in a familiar face!
ET exclusively premieres a never-before-seen moment from season three, featuring Melissa Benoist, Chyler and Chris Wood.
The network's upcoming three-show crossover event will also feature Tyler Hoechlin's return as Superman.
The CW superhero drama revealed several new characters for its fourth season at Saturday's Comic-Con panel.
The CW is dropping some big news about your small screen favorites!
Kreisberg is the executive producer of 'Supergirl' as well as its fellow CW/DC Comics shows 'Arrow,' 'The Flash,' and 'Legends of Tomorrow.'
Supergirl is showing her true strength.
