High School Musical, the hit TV movie that has spawned multiplatinum soundtracks, blockbuster DVDs, a sold-out tour, and thousands of screaming preteens, isn't going away anytime soon.

The cast of High School Musical

That's the word from Disney Channel Worldwide president Rich Ross, who told the Hollywood Reporter yesterday that work has already begun on a script for High School Musical 4--even though filming has yet to begin on High School Musical 3.

"We are writing High School Musical 4," Ross said after a presentation at a midtown Manhattan recording studio.

The cast, including stars Vanessa Hudgens, Zac Efron, Ashley Tisdale, Lucas Grabeel, Corbin Bleu, and Monique Coleman are currently preparing for High School Musical 3: Senior Year, which is set to begin filming in two weeks in Utah.

But while Disney is already looking past the third edition of the series, which is scheduled to hit theaters in October, some of the cast members might not be back.

"[High School Musical 3 is] "going to be the farewell to the East High Wildcats for a while," Efron told MTV News in January. "It's the third act. This is the legacy that we leave...I think it's going to be a good way to go out with a bang."

Ross hinted at the possibility that some of the cast might not return. "Are we going to have all the cast back? Probably not," Ross said. "Will we have some of them? I hope so."

The premiere High School Musical 2 was watched by 18.6 million viewers, shattering cable TV records.