Christopher (The Little Drummer Boy)
From Tardis Wiki, the free Doctor Who reference
Christopher was the twin brother of Robert.
Christopher died from cancer when he was eight years old. Robert, having spent several years time travelling, was returned to 1966 by the First Doctor where he took Christopher's place.
The Doctor took Christopher to Mars before he died, allowing him to see the Earth from space. (PROSE: The Little Drummer Boy)
