Therefore, its known narrative elements are not a part of the Doctor Who universe as we, on this Wiki, choose to define it. It may have been the basis for a similar story in another medium, however — and that story may indeed be valid.
Illegal Alien was an unproduced Seventh Doctor television story. It was originally planned for season 26, but was cancelled because another World War II story, The Curse of Fenric, was on the schedule. The episode was pencilled in for season 27 before the series was cancelled. This story was to feature a redesign of the Cybermen, having a more slender and alien look based on concept art by Mike Tucker. The author eventually adapted it into the novel Illegal Alien. (DOC: Doctor Who: Endgame)