Jenna Dewan-Tatum, the "Witches of East End" star and wife of "Magic Mike" himself Channing Tatum, has joined the cast of CBS' freshman drama "Supergirl". The story follows Kara Zor-El (Melissa Benoist) who escaped Krypton amid its destruction years ago. Since arriving on Earth, she has been hiding the powers she shares with her famous cousin.