With the casting of Peter Capaldi as the 12th Doctor, fans immediately discovered that Capaldi had played two other roles in that universe. The first being Lobus Caecilius from the episode “The Fires of Pompeii,” and the second being John Frobisher from the Doctor Who spin-off, Torchwood. While some people would have written this off as coincidence, many fans thought there could be a connection. Indeed, some people have a hard time accepting that you can have two people that look exactly the same, much less three. And so speculation of a connection begins.
First of all, let me say that I think Capaldi was cast because he was the right actor, with the exact performance that Moffat and crew wanted. I do not think they cast him because they wanted to tie his character with the previous characters he had portrayed. No, he was simply the best actor for the job. That said, I think the writers of Doctor Who could, and probably will, retcon these appearances. The writers of Doctor Who are some of the best at retconning. They have to be to keep the continuity of Doctor Who straight. In fact, they’ve already done a little retconning on this particular issue.