High School Musical 3 hasn't even started filming and won't hit movie theaters until fall, but another sequel is already in the works! "We are writing High School Musical 4," confirmed Disney Channels Worldwide President Rich Ross. "It's likely to be a TV movie, unlike High School Musical 3: Senior Year." However, it's too early to tell if stars like Zac Efron, Vanessa Hudgens and Ashley Tisdale will make it back for the fourth installment. "Are we going to have all the cast back? Probably not," said Ross. "Will we have some of them? I hope so." HSM 3 starts filming in Utah in two weeks.