The series 15 trailer briefly introduced us to new Doctor Who companion Belinda Chandra, played by Varada Sethu, and confirmed the return of familiar faces Millie Gibson as Ruby Sunday, Jemma Redgrave as UNITs Kate Lethbridge-Stewart, Ruth Madeley as Shirley Anne Bingham, Bonnie Langford as Mel Bush, and Anita Dobson as the mysterious Mrs Flood. But who else will be joining the Doctor as guest stars for the new eight-episode series?Below, weve collected the names confirmed so far, including not one but three members of the cast of Apple TV+ spy thriller Slow Horses, plus stars from House of the Dragon, EastEnders, Foundation, The Traitors USA, His Dark Materials, and many more. Well update this guide as new guest stars are announced ahead of the new series April 12 start date.Kadiff KirwanThe latest guest star to be announced is Chewing Gum, Black Mirror, This Is Going to Hurt and Slow Horses actor Kadiff Kirwan, who will appear as an as-yet unnamed character in the space-Eurovision episode written by Juno Dawson and teased in the series 15 trailer. Kirwan describes the episode as an intergalactic gargantuan extravaganza thats packed with gravity-defying mastery beyond imagination and promises that its gonna rock your world! We like an overexcited guest star.Freddie FoxStar of The Gentlemen, The Crown, The Great, Year of the Rabbit, and Slow Horses, Freddie Fox will play a baddie set to cause trouble for the Doctor and Belinda in series 15. Described in the official press materials as a fearsome villain from another planet, Foxs character sports a beautiful set of demonic horns to go with his fury, venom and cunning according to showrunner Russell T Davies, whose crazy, bonkers, beautiful vision Fox said he was delighted to join.Christopher ChungAustralian actor Christopher Chung (Waterloo Road, Blitz) is the third Slow Horses alumni to join the new series of Doctor Who (were sure its a coincidence). He plays a character named Cassio and will appear in an episode that Russell T Davies is calling one of the darkest, toughest episodes weve ever made. As for whether Cassio is an ally or an enemy of the Doctor, youll have to wait and see, but I can promise, its one hell of a meeting!Rylan ClarkWho else would host the Intergalactic Song Contest but Mr Showbiz aka Rylan Clark? The TV presenter best known for Big Brother, This Morning and Gogglebox (as well as a couple of less than well-conceived TV quiz shows) will appear in the Juno Dawson-written episode, in which the Doctor attends what looks like the starry final of a Eurovision pastiche. Evelyn MillerFoundation, and Flowers in the Attics Evelyn Miller, who can also be seen in the new series of Gangs of London, joins the Doctor and Belinda in what looks like episode one of the new series. Appearing alongside some shiny red robots with space guns, Miller is seen sporting a pair of the grubby space PJs that the Doctor and Belinda also wear in the episode, as seen in the first-look images.Rose Ayling-EllisOnce rumoured to have been cast as the 15th Doctors companion before Millie Gibson was announced, EastEnders, Ludwig, Reunion and Code of Silence actor Rose Ayling-Ellis joins the cast for episode five, which Russell T Davies calls one of the most frightening episodes weve ever made. Its an incredible performance, says RTD, marked by terror, anger and bravery. Sofa cushions at the ready!Jonah Hauer-KingPictured above in the second series of BBC period drama World on Fire, Jonah Hauer-King was also spotted in the Doctor Who series 15 trailer and is heavily rumoured to be playing Ruby Sundays boyfriend. Hauer-King is known for having played Prince Eric in Disneys live-action The Little Mermaid movie, and for the roles of Harry in World on Fire and Lali in The Tattoist of Auschwitz.Alan Cumming (Voice)Returning to Doctor Who after playing King James I in 13th Doctor-era episode The Witch Finders will be Scottish actor Alan Cumming, seen recently as the host of the US version of reality lie-detector show The Traitors. Cumming will be voicing the role of 1950s cartoon character Mr Ring-a-Ding, a creation who steps out of the screen and causes chaos for the Doctor and Belinda.ALSO APPEARINGStage and screen actor Ariyon Bakare, who recently appeared in BBC drama Mr Loverman, and is known for roles with the RSC, in His Dark Materials, and in Carnival Row.Join our mailing listGet the best of Den of Geek delivered right to your inbox!Irish stage and screen actor Caoilfhionn Dunne, known for Britannia, and wholl soon be seen in Lisa McGees Derry Girls follow-up How to Get to Heaven from Belfast, as well as recently having starred in Disney+ drama A Thousand Blows.French actor Julie Dray (Avenue 5, Ludwig, The Curse) will appear alongside Rylan Clark as an exotic alien presenter of the Intergalactic Song Contest episode. The Good Wifes Kalinda, and Snowpiercer, Blindspot, Under the Bridge and Hijacks Archie Panjabi will appear in an as-yet-undisclosed villain role.Doctor Who season two/series 15 starts on Saturday April 12 on BBC One and iPlayer in the UK, and on Disney+ around the world.