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. It appeared to feature an image of the Sixth Doctor on the cover. He also found The Android Invasion. (COMIC: The Girl Who Loved Doctor Who)

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