Ncuti Gatwa regenerated into Billie Piper in the series finale of Doctor Who on Saturday night. He left the role after playing the iconic character for two series. Piper, who previously played the Doctor's assistant, Rose Tyler, said the opportunity to "step back on that Tardis one more time was just something I couldn't refuse".

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!

The Doctor has just been exterminated – but not by Daleks. After mounting speculation that leading actor Ncuti Gatwa would be leaving Doctor Who, Saturday’s series finale saw him regenerate into the Time Lord’s next incarnation sooner than planned.