The Doctor Who 60th anniversary specials took fans on a trip down memory lane as David Tennant returned as the Doctor, alongside Catherine Tate as companion Donna Noble. The duo first appeared alongside each other in the 2006 Christmas special, "The Runaway Bride," before Donna became a full-time companion throughout Season 4 of Doctor Who in 2008. Tennant's return came as a stark departure from previous stories in which past Doctors have come back, though. Rather than appearing as the Tenth Doctor again, Tennant came back as the Fourteenth Doctor, a brand new incarnation with his old face inexplicably returning.
Source：https://www.cbr.com/doctor-who-60th-anniversary/
