<P> Leigh first appeared on the show during the last two episodes of the third season as Meredith 's half - sister , Lexie Grey . Following Isaiah Washington 's departure who portrayed Preston Burke , it was reported that show 's executives were planning on adding new cast members , such as Lexie . She was officially upgraded to a series ' regular on July 11 , 2007 , for the fourth season . On casting Chyler Leigh as Lexie , Grey 's Anatomy creator Shonda Rhimes said : `` We met with a lot of young actresses , but Chyler stood out -- she had a quality that felt right and real to me . It felt like she could be Meredith 's sister , but she had a depth that was very interesting . '' </P>
<P> Leigh first appeared on the show during the last two episodes of the third season as Meredith 's half - sister , Lexie Grey . Following Isaiah Washington 's departure who portrayed Preston Burke , it was reported that show 's executives were planning on adding new cast members , such as Lexie . She was officially upgraded to a series ' regular on July 11 , 2007 , for the fourth season . On casting Chyler Leigh as Lexie , Grey 's Anatomy creator Shonda Rhimes said : `` We met with a lot of young actresses , but Chyler stood out -- she had a quality that felt right and real to me . It felt like she could be Meredith 's sister , but she had a depth that was very interesting . '' </P>
when does lexie come in grey 's anatomy
when does lexie come in grey 's anatomy
the last two episodes of the third season
the last two episodes of the third season