Hilton, who has signed up to reprise his role as Chris Keller, explained that Schwahn was not expecting the show to get recommissioned.
"One of the reasons why I am such a fan of this last season is because Mark said that last season he thought it might be the last season, so he ended it the way fans wanted it to end," HIlton told E! Online.
"This season he knows it is going to be the last season, and since he already kind of gave the fans their season last time, he said that he really wants to make this season what he wants."
Hilton continued: "He said that since the show is done after this season, he has no-one to impress, he can just do whatever he wants."
Yesterday, it emerged that Chad Michael Murray will reprise his role as Lucas in the final season, while Paul Johansson has already signed up to return.
Elsewhere, Joe Manganiello recently told Digital Spy that he "would love" to return to One Tree Hill.
One Tree Hill will return in midseason on The CW.
> Hurricane Irene shuts production on One Tree Hill
> Read more coverage of One Tree Hill