Welcome back to Doctor Who, Billie Piper! The British sci-fi series just shocked fans when, in the Season 2 finale, Ncuti Gatwa ‘s Doctor regenerated — and the Sixteenth Doctor appears to be played by none other than Piper!

The season finale of Doctor Who, ‘The Reality War,’ was shocking for many reasons. However, the biggest surprise involved an appearance by actress Billie Piper, who played Ninth and Tenth Doctor companion Rose Tyler.

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".