Doctor Who: 12 Cool Details Revealed In Steven Moffat's Blink Commentary
5. Young Billy And Old Billy Were Almost Played By The Same Actor
While Michael Obiora and Louis Mahoney ultimately ended up playing Billy at different ages, there was initially a lot of talk about using one actor instead of two.
While discussing Billy during the commentary, Moffat revealed that the production team found it difficult to decide whether to go with a single actor (and use prosthetics to make him look older) or two actors.
In the end though, then-showrunner Russell T Davies (along with producer Phil Collinson) felt that audiences wouldn't buy the emotion of Billy's death if he was played by an actor in makeup, because no matter how good that makeup might be, it would still be a distraction. And so, Obiora and Mahoney were cast instead.