The Thirteenth Degree

 was the subtitle of the 11th and 12th series of Doctor Who that featured Iwan Rheon as The Doctor's thirteenth incarnation and Carrie Preston as his new companion, Deidre Havilland.

Details
After it was announced in January 2017 that Peter Capaldi would leave his role of The Doctor, rumours of his successor began to surface. Shortly after, it was confirmed that Pearl Mackie and Matt Lucas would not return for a second series as companions. In July 2017, at the conclusion of the tenth series, Iwan Rheon was confirmed as Capaldi's successor. Later in the year, American actress Carrie Preston was announced as The Doctor's new companion, starting in the 2017 Christmas special.

Filming began on the Christmas special and the eleventh series in October 2017, concluding 5 months in March 2018 - just a week before the series premiere.