With "The Giggle," Doctor Who concluded its run of 60th Anniversary specials, officially introducing Ncuti Gatwa as the Fifteenth Doctor. The three specials marking the sci-fi series' 60th year saw the return of David Tennant and Catherine Tate as the Fourteenth Doctor and Donna Noble, as well as the return of former showrunner Russell T Davies and much of the production team who worked on Doctor Who when it was first brought back to television in 2005. While "The Giggle" concluded Tennant's and Tate's second stint as the stars of the show, Davies will be sticking around to relaunch Doctor Who for a new generation, with Gatwa now in the lead role.
Source：https://www.cbr.com/doctor-who-60th-anniversary-ncuti-gatwa-era-setup/
