In early July 2007, it was announced that she would be the new companion in Doctor Who (2005), reprising her role as Donna Noble from
the 2006 Christmas episode. She joined David Tennant (the Doctor) and Freema Agyeman, the previous companion, halfway through the fourth series. Three years Tennant's senior, she is the first companion older than the actor playing the Doctor she accompanies.
On accepting her new position as the Doctor Who companion: I am
delighted to be returning to Doctor Who. I had a blast last Christmas
and look forward to traveling again through time and space with that
nice man from Gallifrey.