Re: Moffat Talks 13th, sorry, 12th Doctor
I'm perfectly happy to accept that sometimes the Doctor's brain remembers people he sees on this travels and subconsciously incorporates elements into a new regeneration. That makes enough sense, it doesn't need further explanation.
We already know that when Romana regenerated, she consciously chose to model her appearance on Princess Astra (Lalla Ward) from the previous adventure.
-- Christopher L. Bennett's blog and webpage