 Rose Tyler is mentioned several times in this episode. Jack tells  the Doctor that he saw Roses name on the list of the dead after the  Battle of Canary Wharf, but the Doctor assures him that she is safe,  together with her mother and Mickey, and is trapped in a parallel  world. Jack later tells Martha about being left on Satellite 5 by  the Doctor, and comments that the Doctor only saves blondes. Jack  mentions that he looked in on Rose while she was growing up. Near  the end of the episode, Jack and the Doctor discuss Jacks  invulnerability/immortality, and the Doctor tells Jack that Roses  fallible humanity is responsible both for Jacks resurrection as  well as his inability to die ever again.