Bill Potts: Do you know what the hardest thing about knowing you was?
Twelfth Doctor: My superior intelligence. My dazzling charisma. Oh! My impeccable dress sense.
Bill Potts: Letting you go. Letting go of the Doctor is so, so hard.
From Doctor Who – Season 11 Episode 0: ‘Twice Upon a Time’ (11×00 / Christmas special 2017)