Merritt Patterson will be a series regular on Ravenswood.
According to The Hollywood Reporter, the actress (Kyle XY, Supernatural) will portray Tess on the Pretty Little Liars spinoff, the former best friend of Elizabeth Whitson's Olivia. This character will NOT be one of the five town residents involved in the show's mysterious curse.
Patterson joins a Ravenswood cast that includes Whitson; Brett Dier as Olivia's twin; and Tyler Blackburn as Caleb.
Ravenswood will premiere this October on ABC Family, while Pretty Little Liars Season 4 kicks off June 11.
UPDATE: ABC Family has announced that Patterson will now play Olivia and Whitson is actually off the series.