Ncuti Gatwa had a Doctor Who debut unlike any other Doctor. The third and final Doctor Who's 60th Anniversary special, "The Giggle," saw David Tennant's Fourteenth Doctor undergo the series' first bigeneration, splitting in two to give life to Gatwa's Fifteenth Doctor. The new Doctor quickly clarified for his confused onlookers that he had bigenerated, a process that he claimed was supposed to be a myth. However, in true Doctor Who fashion, this myth proved to be far more real than the Doctor had thought. However, the history and the origins of this ancient myth of the Time Lords are yet to be explored.
Source：https://www.cbr.com/doctor-who-bigeneration-before-60th-anniversary/
