The Twin Dilemma (The Girl Who Loved Doctor Who)

The Twin Dilemma was a self-described "part of [ the Doctor's] life". The Eleventh Doctor came across this story as he browsed through Ally's Doctor Who DVD collection. He also found The Android Invasion. (COMIC: The Girl Who Loved Doctor Who)

Behind the scenes
The Twin Dilemma is a Sixth Doctor serial, the first full story to feature Colin Baker as the Doctor.