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 so after he started working on the fourth series. He returned to the fourth series because he thought his character had gained momentum by the end of the last series, and wanted to see where it would go next. The crew desired Adam to transition from a "happy-go-lucky" persona to one that would make it difficult for him to be jovial towards the end of the fourth series; this involved Fiona's demise.