The first major piece of casting is in place for The CW's possible spinoff to "Gossip Girl."

According to The Hollywood Reporter, Krysten Ritter has been cast as Carol Rhodes, sister to Lily Rhodes, the young woman who will eventually grow up to be Lily van der Woodsen (and Kelly Rutherford on "Gossip Girl").

The backdoor pilot will air as the May 11 episode of "Gossip Girl" and will be written by series co-creators Josh Schwartz and Stephanie Savage. Set in Los Angeles in the '80s, the spinoff will focus on Lily leaving her Montecito private school and moving in with her sister Carol in the San Fernando Valley.

Ritter is a familiar face for CW audiences from her work on "Gossip Girl" and "Veronica Mars." Her most recent TV credits include several episodes of FOX's "'Til Death," as well as a multi-episode arc on the upcoming second season of AMC's Emmy-winning "Breaking Bad." She'll also be seen on the big screen in the upcoming "Confessions of a Shopaholic."