Ever since the Supergirl TV series was first reported last month, the project has sped through development, with CBS picking up the show in mid-September. Casting is currently under way for the title character, Kara Zor-El, along with a character created specifically for the series, Kara's foster sister.

TV Line has acquired a casting breakdown for the series, which confirms plot details that were released last month. Much like in the DC Comics, Kara Zor-El will be sent from her dying home planet of Krypton to Earth at the tender age of 12, where she is taken in by the Danvers family.

RELATED: Is Sasha Calle's Supergirl Getting an HBO Max Spinoff Series After The Flash Movie?

Her new family warns her early on about using her powers, which causes Kara Danvers to repress her gifts until the age of 24, when she suddenly puts her powers on display during an "unexpected disaster." For the first time in her life, she begins using her abilities to help those in need as she "earns her super moniker." The series is currently looking for actresses between the ages of 22 and 26 to play the 24-year-old character.

Supergirl producers are also casting for Kara's 26-year-old foster sister, Alexandra "Alex" Danvers, described as "gorgeous, brilliant and science-minded." The casting breakdown reveals that Alex grew up being jealous of Kara's abilities, which pushed her to learn everything about, "alien anthropology, sociology and culture." She now works for a secret government organization and will face "mundane and super challenges" alongside her sister.

The Supergirl pilot script was co-written by Greg Berlanti (Arrow, The Flash) and Ali Adler, who both previously worked on the ABC superhero series No Ordinary Family. The writers will also executive produce alongside Sarah Schechter.

What do you think about Supergirl having a foster sister? It has never been revealed if the show plans on bringing in Kara's Kryptonian cousin, Superman, but perhaps we'll find out more in the near future.