The creator of hit series Glee has admitted he will need to axe a mix of the main characters in the next series.Executive producer Ian Brennan says series three will be the end of the road for some of the pupils.The cuts could include Cory Monteith (Finn Hudson), award-winning actress Lea Michele (Rachel Berry) and Chris Colfer, (Kurt Hummel).Brennan said, "We aren't going to change the entire cast, but some of the cast will graduate. Changes I just think we would be missing a beat if we didn't acknowledge the fact that a huge part of high school is graduating from high school, and that's going to give us a lot of stuff to write in season three."Every time we bring in a new character it's worked out really well. We've been very fortunate."Admitting there are likely to be big changes, he added, "We get to sort, of start new - we get to bring in new characters and write new storylines. So bringing in new characters will allow us a little more flexibility and will add to the longevity of the show.