Most teen series struggle as their lead actors age, but EW has learned that TeenNick has just begun production on the 12th(!) season of Degrassi, which will premiere this summer and contain the show’s 300th episode. The secret to the Canadian drama’s success: allowing its high school seniors to graduate and disappear instead of following them into the AARP. To that end, Degrassi will introduce four new characters — Campbell (grade 10), Mike (grade 12), and siblings Luke and Becky (grade 11). But before that, season 11 will wrap up with the return of a fan favorite. Recent grad Holly J. (Charlotte Arnold) drops in for the final two episodes to help her best friend, Fiona (Annie Clark), with relationship and family troubles.