PeterCapaldi’sfinalepisodeofDoctorWhothisChristmaswillfeaturePearlMackieasBillPottsandbecalledTwiceUponaTime,itwasrevealedthisevening(23July)duringacastpanelatSanDiegoComicCon.ViewerswillhavetowaituntilChristmastodiscoverexactlyhowBill,whowillappearthroughouttheepisode,makesherreturn.
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