'Scrubs' creator Bill Lawrence decided last season to kill off Nurse Laverne Roberts, but he promised the actress who played her, Aloma Wright, that if the show came back for another season, he would bring her back as well - as Laverne's twin sister.
And so a grand Toobworld tradition is upheld - that of the identical twin. I'm not so sure the character of the sister will be taking it further and be an evil twin as well - the gold standard of the tradition right up there with "identical cousins" - but she will be the polar opposite of Laverne. Whereas Laverne was God-fearing and God-loving, Shirley will be single, alchoholic, and someone who turned her back on religion. She'll also be sporting a wig to make her physically different from her "sister" as well.
Hunh. Laverne & Shirley. Just noticed that in-joke as I typed the story up. Getting slow in my old age.