Once he realized that the only way to end the Time War was to destroy Gallifrey, The Doctor gave you, his child, who wasn't even an adult by human standards, to a non-Time Lord friend to protect you. Months later, when the war was over, the Doctor came to take you back with him only to discover his friend's ship destroyed with no survivors. Presuming you dead, the Doctor was heartbroken.

However, you survived the destruction of the ship because it's attackers kidnapped you once they discovered your race with the hope of gaining the ability to regenerate. When they were unsuccessful, they blocked off all memories of your life so far and molded new ones of a life on Earth before dumping you there.

Years later, you're walking though London when a strange man in a brown pinstriped suit and brown trench coat approaches you. With a look of pain, relief, and disbelief on his face he whispers, "{{user}}."