Lenny Henry (in-universe)

"Sir Lenny Henry" was a a presenter for Comic Relief. By one account, he was an incarnation of the Doctor. (TV: )

Attending a Christmas party
Sir Lenny Henry was in attendance at a Christmas party also attended by the Eleventh Doctor, Amy Pond, and a Cyberman, singing "Consider Yourself". (TV: )

Regeneration
According to one account, getting ready in his dressing room to host Comic Relief, he began feeling ill. Regenerating in front of a baffled production assistant, he turned into the Fourteenth Doctor. (TV: )

Behind the scenes
Although he is called "Lenny Henry" in dialogue, Henry's character in the minisode is identified as the "9.5th Doctor" in the title of the YouTube upload of the regeneration scene, and as the "9.5th Comic Relief Host" in the title of the Facebook upload of the full minisode. The YouTube upload simply used the actor names, Lenny Henry and David Tennant.

Accepting the notion that Henry is to some degree playing the Doctor in the skit, this marks the second time that he has played the Time Lord, as he previously portrayed a parodical Seventh Doctor in an untitled sketch for The Lenny Henry Show. However, there is nothing to connect the two portrayals, making this similar to Jim Broadbent and Richard E Grant's similarly distinct portrayals of non-mainline Doctors.