David Tennant's Fourteenth Doctor's ability to bi-generate again depends on whether the Toymaker was responsible the first time. The Toymaker may have unknowingly helped the Fourteenth Doctor to bi-generate. Doctor Who needs to confirm whether the Doctor's ability to bi-generate was a one-time deal.

The Doctor Who 60th-anniversary specials included a huge addition to the show's lore by having the Doctor split into two autonomous beings, but it's possible that the famous Time Lord may never be capable of repeating the feat. David Tennant's return to Doctor Who placed the actor twice in the Doctor's timeline. While Tennant originally played the Tenth Doctor, who regenerated into Matt Smith's Eleventh, Tennant's Fourteenth Doctor is still present despite handing the baton to Ncuti Gatwa's Fifteenth. Doctor Who's shocking bi-generation twist was something no one saw coming, but it also may have been a one-off event.

The Fourteenth Doctor is...