The Snowmen (in-universe)

In Red Nose Day 2013, clips from an episode of Doctor Who played on a screen behind Claudia Winkleman, Dermot O'Leary, and the Eleventh Doctor. The story featured the Doctor as portrayed by Matt Smith, and an individual portraying a character who resembled Walter Simeon. (TV: The Doctor Appears)

Important note
This is a in-universe counterpart of the real world Doctor Who television story The Snowmen that exists within the Doctor's universe. It was briefly seen in the television story The Doctor Appears, where Dermot O'Leary surprises his co-star Claudia Winkleman with a surprise visit from the Eleventh Doctor, who she clearly idolises.