Kiefer Sutherland has said that returning to his 24 character Jack Baeur has been difficult and he is harder to play than ever.
The actor last starred as the CTU agent four years ago and has found the change in Bauer's character a difficult one to get his head around.
He told The TV Page, "He has very much been operating on his own so he does not have the same kind of loyalty as a character that he might have in the previous eight seasons, certainly with regards to Chloe.
"I think he has had enough bad things happen to him that he really doesn't trust anybody. And so I think he is even harder a character now that he ever was. Trust me, in the last few seasons of 24 he was a very hard guy [to play] but he is even harder now."
But where has Jack been for the last four years? Sutherland explained, "He has been underground, hiding and had kind of accepted the fact that that was going to be the rest of his life. And he intercepted some intelligence that puts him in motion for this season."
The 47-year-old also detailed his new fitness regime to get back into top shape, "I started training five months ago. I do a run every day, lighter weights, heavy repetitions... Everything I can for endurance. Because it is a grinding show and I am not getting younger."
24: Live Another Day will premiere in the US on May 5 and will air on Sky One shortly after.