In the climax of Saturday’s Finale of “ Doctor Who ” Series 14, Gatwa’s Doctor regenerates into Billie Piper, who previously played companion Rose Tyler in Series 1 (2005) and Series 2 (2006). She also made a brief appearance as Rose Tyler in Series 4 (2008) and was in the “Doctor Who” 50th anniversary special in 2013.

Ncuti Gatwa has left his role as the Doctor after playing the iconic character for two series on Doctor Who. At the end of this evening's series finale, Gatwa regenerates into Billie Piper, who previously played the Doctor's companion, Rose Tyler.

Ncuti Gatwa has left the sci-fi series, "Doctor Who," after two seasons and former franchise co-star Billie Piper is taking his place.