The Watcher (Logopolis)

During the moment that the Doctor's fourth incarnation regenerated into his fifth, The Watcher manifested as a physical projection. Eerie in appearance, the Watcher had a white, featureless, unform face and white clothes. He silently appeared observing events on Earth initially and conferred with the Doctor. Later, he transported Nyssa from the doomed Traken to Logopolis] to safety.

At the moment of the Fourth Doctor's regeneration, the Watcher merged with the body. (DW: Logopolis)

Another Time Lord, K'anpo Rimpoche, had apparently manifested his future regeneration as his assistant, Cho Je. (DW: Planet of the Spiders)