Neil Patrick Harris has joined BBC's Doctor Who and is currently filming scenes set to air in 2023. The How I Met Your Mother star, 48, is playing a mystery character yet to be revealed and will join the hit BBC One series as part of the show's 60th anniversary.Teasing Neil's debut and role, showrunner Russell T Davies said: "It’s my huge honour to open our studio doors for the mighty Neil Patrick Harris… "But who, why, what is he playing? You’ll just have to wait. But I promise you, the stuff we’re shooting now is off the scale.