Lenny Henry (in-universe)

As "Sir Lenny Henry", the apparent 9.5th Doctor, and 9.5th Comic Relief Host was a presenter for Comic Relief.

While 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 a new Doctor (NOTVALID: Lenny Henry Regenerates into David Tennant) identical to the Fourteenth Doctor into whom the Thirteenth Doctor regenerated into in another account. (TV: The Power of the Doctor)

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 Short 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 this skit, this makes the second time that he did so, as he previously portrayed a parodical Seventh Doctor in an untitled sketch. However, there is nothing to connect the two portrayals, making this similar to Jim Broadbent and Richard E Grant's two distinct portrayals of non-mainline Doctors.