Fall of the Eleventh

The Eleventh Doctor, having expended the 12-regeneration life cycle beginning with the First Doctor, was enabled to undergo what he called "regeneration number thirteen" into the Twelfth Doctor after being provided with additional regeneration energy by the Time Lords at the end of the Siege of Trenzalore. (TV: The Time of the Doctor) This event was prophesied as the Fall of the Eleventh by Dorium Maldovar. (TV: The Wedding of River Song)

However, in a timeline viewed by the Doctor at an earlier date, the Doctor was seen to have finally died, with their TARDIS growing its exterior dimensions and acting as his grave. (TV: The Name of the Doctor)

Anticipation
According to one account, the Tremas Master claimed that the Valeyard was the Doctor's "penultimate reincarnation… somewhere between [their] twelfth and thirteenth regenerations". (PROSE: The Ultimate Foe)