'Doctor Who' regenerates as Ncuti Gatwa leaves and Billie Piper returns

Ncuti Gatwa, the first Black actor to play the lead role in British sci-fi show "Doctor Who", departed the series on Saturday in a season finale that saw familiar face Billie Piper reappear in his place.

The Doctor, who travels through time in what appears to be a blue police telephone box, has the ability to regenerate, allowing a number of actors to play the role since the series was first broadcast in 1963.

In a surprise twist, Gatwa regenerated into the form of Billie Piper - who played one of the Doctor's companions in 2005 and 2006.

"I've loved every minute of it, but now is the time to hand over the keys to that beloved blue box and let someone else take control and enjoy it every bit as much as I have," said Gatwa, 32, who was announced as the 14th Doctor three years ago.

Piper, 42, won plaudits for her portrayal of Rose Tyler, an instrumental character in the show's successful 2005 revival after a 16-year hiatus.

"To be given the opportunity to step back on that TARDIS one more time was just something I couldn't refuse," Piper said, referring to the Doctor's police box.

Showrunner Russell T. Davies said the "why and who" behind Piper's return to the show had yet to be told.

"After 62 years, the Doctor's adventures are only just beginning!" Davies said.