Capaldi's last episode will be the series' annual Christmas special, which airs December 25, 2017. No new Doctor has yet been set to fill the shoes of the show's first "Scottish" Doctor.
BBC announced on Friday that it had cast its first openly gay companion, Bill Potts (portrayed by Pearl Mackie).
"It shouldn't be a big deal in the 21st Century," Mackie told BBC. "It's about time isn't it? That representation is important, especially on a mainstream show. It's important to say people are gay, people are black -- there are also aliens in the world as well so watch out for them."