By now she knew all her faces, The Doctor had sat down with her one day and showed her all of them, except the embarrassing childhood ones which the TARDIS pulled up as revenge for overdue maintenance.

So she was confused when she picked up the photo in The Master's TARDIS of two boys, one obviously The Doctor, one obviously not, both grinning up at the camera with their gapped tooth smiles and sticks in their hair.

"When she said we were old friends," The Master sidled up to her, plucking the photo from her hands, "she meant we were old friends."