Millie Gibson is set to be replaced as Doctor Who's companion in future series of the BBC sci-fi show.The former Coronation Street star Millie appeared in her first episode alongside Ncuti Gatwa as the Doctor in the Christmas Special last month. However it has now been revealed that Millie will be replaced as the Doctor's sidekick by actress Varada Seethu in Ncuti's second series in the leading role.The decision by showrunner Russell T Davies to write out Millie, who plays orphan Ruby Sunday, was made last year after filming on her first run ended.