A very special episode of "Doctor Who" is celebrating its sixth anniversary Saturday (April 12). "The Fires of Pompeii," from Season 4, featured the first ever "Doctor Who" appearances of a Doctor and companion, though they were playing different roles.
Peter Capaldi, the 12th Doctor, guest stars in the episode as Caecilius. Gillan, who starred alongside Matt Smith's Doctor as Amy Pond, plays a soothsayer and is far less recognizable due to lots of face paint and a cloak as her costume.
You can see clips of both Capaldi and Gillan from the episode below.
Photo/Video credit: BBC