In Logopolis, the last story of the Fourth Doctor's tenure, we meet the Watcher, a mysterious character, white from head to toe, who is revealed to be the interim stage of the Doctor's regeneration from the Fourth to the Fifth Doctor. He interacts with a few other characters during the story: first the (Fourth) Doctor himself, then Adric and the rest of the Tardis crew, and he even flies the Tardis at one point.
Where did his clothes come from? Throughout the regeneration process the Doctor is wearing the same clothes; the final shot of the last episode shows the Fifth Doctor sitting up, still wearing the Fourth Doctor's clothes. But the clothes the Watcher is wearing bear no resemblance to those of the Fourth Doctor.
(I can appreciate that if the Watcher had appeared wearing the same clothes as the Fourth Doctor, or a white copy of them, then it would have given the game away who the Watcher was at the beginning.)