Doctor Who: 9 Ways To Kill The Doctor Permanently

9. The Poison Of The Judas Tree

It's pretty hard to stay one step ahead of the Doctor, because the character is normally several dozen steps ahead of everyone else.

That said, the Eleventh Doctor was completely outplayed by River Song in the Series 6 episode Let's Kill Hitler, and if not for her last-minute change of heart, she would actually have ended up cancelling his regeneration and killing him outright.

This early version of River is intent on murdering the Doctor due to her brainwashing, which she tries (and fails) to do using weapons like guns and knives. Soon after though, she manages to succeed in delivering a fatal blow by giving the Doctor a cheeky kiss on the lips, infecting him with her poisonous lipstick.

It's later revealed that the Doctor has been contaminated with the poison of the Judas tree, which - as the TARDIS interface informs him - has "disabled" his ability to regenerate. The interface also adds that there's no cure, and that he'll be fully dead in around half an hour. Very grim indeed.

The Doctor is only saved when River decides to use up her entire stock of regeneration energy to heal him, but if this hadn't happened... then he was a goner.