Something I have noticed recently in the Doctor Who universe are the companions of the Doctor (specifically the actresses that act as them) have a cameo appearance in the season before.
For example, in Season 2 of the new series of Doctor Who, a member of the Torchwood team was Adeola Oshodi (played by Freeman Agyeman). Freema, whom joined the TARDIS team as Martha Jones in Season 3. However in Season 3, there wasn’t any new companions appearing then.
In Season 4 when Donna Noble (played by Catherine Tate) and the Doctor went to visit Pompeii, a mysterious Soothsayer was watching them. Karen Gillan (the Soothasayer mentioned) was Amy Pond, the Doctor’s last companion in Seasons 5,6 &7.
Can you guess who the next one is?? 🙂