Tenth Doctor's regeneration

"I don't wanna go."

- The Tenth Doctor's last words

The Tenth Doctor, who had previously regenerated and kept the same face during the Planetary Relocation Incident, (TV: Journey's End) met his regeneration into the Eleventh Doctor as a result of radiation poisoning intentionally incurred in order to save the life of Wilfred Mott after thwarting 's Final Sanction. (TV: The End of Time) By later accounts, this was the twelfth and final regeneration of the 12-regeneration life cycle beginning with the First Doctor. (TV: The Time 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)

After the Doctor and Donna Noble aided in the revolution of the Ood in 4126, Ood Sigma ominously warned the Doctor that "[he thinks his] song must end soon". (TV: Planet of the Ood)

During the Planetary Relocation Incident, the Doctor was fatally shot down by a single Dalek, triggering a regeneration. However, he was able to undergo the process without changing his appearance, by siphoning the remaining Artron energy into his severed hand after it had healed him. This later led to the creation of the Meta-Crisis Doctor. (TV: The Stolen Earth/Journey's End) By later accounts, this counted as the eleventh and penultimate regeneration of the Doctor's first regeneration cycle. (TV: The Time of the Doctor)

When he met Jackson Lake, a 19th century man who believed himself to be the Doctor after having picked up an infostamp, the Doctor initially assumed Jackson to be either his next incarnation or the "next but one". (TV: The Next Doctor) By a later account, however, he assumed the Twelfth Doctor to be his next and final incarnation, knowing his next regeneration to be his last. (COMIC: Vortex Butterflies) In an alternate timeline, in an encounter between him and his two immediate successors, the Tenth Doctor was skeptical of his twelfth incarnation's identity, believing "this man [could not] exist. Shouldn't exist!" (COMIC: Four Doctors) After he brought The 200 London bus and its passengers back through the wormhole from San Helios, Carmen, a passenger with precognitive psychic abilities, echoed the words of Ood Sigma, telling the Doctor that his song was ending, adding: ""It is returning. It is returning through the dark, and then Doctor...oh but then... he will knock four times.""

- TV: Planet of the Dead

The Nun, formerly the Monk, posed as a regenerated Doctor to Anya Kingdom and Mark Seven after first using a psychic cloak to assume the form of the Tenth Doctor before faking his regeneration. (AUDIO: Buying Time, The Wrong Woman)

After the Doctor's radical actions as the "Time Lord Victorious" led Adelaide Brooke to commit suicide, his sobering realisation that he had gone too far caused him to see a vision of Ood Sigma, to whom the Doctor fearfully asked if it was time for his death. After the vision had disappeared, the Doctor returned to the TARDIS and, following some contemplation, defiantly exclaimed "no", as he put the ship into flight. (TV: The Waters of Mars)

Shortly before his regeneration, the Tenth Doctor saw a solitary pale Watcher observing him; shortly after the TARDIS dematerialised, the Watcher also disappeared. (PROSE: The Advent of Fear) The Doctor encountered his successor in a dream, who assured him that they would be fine. (COMIC: To Sleep, Perchance to Scream)

As the Doctor parted ways with Mason Valentin, he admitted that there was something he had been avoiding, adding that, like the titular character of The Snowman, after all the "flying around, having fun, and doing the impossible", his time was up. (PROSE: The Doctor on My Shoulder)

Circumstances
When Gallifrey appeared in the sky above Earth, there was a tremendous kerfuffle. A man became trapped in the control booth, and Wilf freed him, himself becoming trapped. Once the Time Lords had been dealt with and the Master had died, the Doctor realised that the Nuclear Bolt had been left running, had gone critical, and was about to overload. After complaining to the universe, stating he "could do so much more", he entered the booth to save Wilf, and was blasted full of radiation.

He then got up, brought Wilf back home, and, upon being questioned as to where he was going, stated "To collect my reward."

Final reward
The Doctor managed to hold off his regeneration for some time, in order to embark on a final set of trips in order to check in on all of his former companions. (TV: Death of the Doctor)

He checked in on Martha Jones and Mickey Smith, Sarah Jane Smith and her son Luke, Jack Harkness, Verity Newman - a descendant of Joan Redfern - and once more on the Nobles. (TV: The End of Time)

He also had final meetings with Novice Hame, (WC: The Secret of Novice Hame) Heather McCrimmon and Wolfgang Ryter, (COMIC: Lucky Heather) George Litefoot, (AUDIO: The Jago & Litefoot Revival) and Christina de Souza. (AUDIO: Last Chance)

He also watched Jo Jones sail down the Yangtze River in a tea chest. (TV: Death of the Doctor)

Finally, he returned to the Powell Estate in the early hours of 1 January 2005 to watch Rose Tyler, before she started her travels with him. The two briefly interacted when she noticed him wincing in pain in the dark, assuming him to be drunk. The two wished each other a Happy New Year before they parted ways, but not before he told her that he reckoned she was going to have a great year. (TV: The End of Time)

Regeneration
After Rose left, the pain overcame the Doctor and he stumbled to the TARDIS, seeing a vision of Ood Sigma who assured him that though "this song" was ending, "the story" would continue. Taking off into Earth orbit, the Doctor proclaimed "I don't wanna go" before his state of grace expired and he began his twelfth and final regeneration, unleashing a massive burst of energy that set the console room aflame. (TV: The End of Time)

Aftermath
The Eleventh Doctor's first priority was to inspect his new body, making sure he still had all vital body parts such as legs, arms, hands, and so on, before he briefly struggled to remember that the now-heavily damaged TARDIS was crashing. He enthusiastically threw himself into navigating the ship (TV: The End of Time) through the skies of London in April 1996, before he crashed into the back garden of a young Amelia Pond. (TV: The Eleventh Hour)

Legacy
When Sarah Jane Smith first met the Eleventh Doctor, she inquired about the Tenth Doctor's regeneration, the Eleventh Doctor telling Sarah and Jo Grant about his previous incarnation's visiting all his companions. (TV: Death of the Doctor)

When Mr Clever tried to upgrade the Eleventh Doctor, the Time Lord allowed the Cyber-Planner to access his memories about past regenerations, Mr Clever glimpsing the Tenth Doctor's regeneration. (TV: Nightmare in Silver)

Behind the scenes
Four different takes of the Doctor's final words were recorded, in which the emotion and grief was pushed further with each delivery. Said deliveries ranged from blunt and almost emotionless, to the Doctor being on the verge of tears. (CON: Allons-y!)