A familiar face to “Doctor Who” fans is rejoining the long-running British sci-fi series as Ncuti Gatwa exits the lead role after two seasons. In Saturday’s season finale, Gatwa’s Time Lord regenerated and fans got a glimpse of Billie Piper,

Warning! The following contains spoilers for the Doctor Who episode "The Reality War." Stream it with a Disney+ subscription, and read at your own risk! While the surprise casting of Billie Piper as the next star of Doctor Who helped lessen the sting of Ncuti Gatwa's Doctor regenerating,

Ncuti Gatwa's shock regeneration is followed by an even bigger surprise as the show welcomes back a popular star of TARDIS past. BEWARE! Spoilers ahead!