He felt especially so after he started working for the fourth series. He returned to the fourth series because he thought his character took off by the end of the last series, and wanted to see which direction he would go to next. The crew wanted Adam to go from a "happy-go-lucky" figure to wanting him to deal with things that would make it hard for Adam to be jokey towards the end of the fourth series; this involved Fiona's death.
He felt particularly enthusiastic about his role in the fourth series, as he believed his character had gained momentum by the end of the previous season and wanted to see where it went next. The crew wanted Adam to shift from a carefree personality to one that would make him less jovial, culminating in Fiona's death.