This may be old news but I'm sharing it anyway.
I am eager the explanation and or mystery that RTD and Moffat came up with to explain the 3 characters who share Capaldi's likeness in the Whoinverse .
The 3 characters are
Lucius Caecilius Iucundu from Doctor Who "The Fires of Pompeii
John Frobisher from the Torchwood mini series Children of Earth
and the 12th Doctor