Wait, I just realized. Was Yaz the only companion who was there for both the beginning and end of her Doctor’s life? That so sweet. Well, unless you count the Brigadier as a companion, but still
No, Rose was there for Nine's entire run.
His entire tv run, yes, but not his immediate post-regeneration. Even if that happened really soon before the episode, he has definitely been running around in a few adventures first
In 'Rose' he sees his reflection for the first time and comment on his new appearance so unless he has been avoiding mirrors for a long time this has to be his first post-regeneration adventure.

















