In the Doctor Who episode Journey's End we are introduced to possibly the 11Th incarnation of the Doctor. For the first time the Doctor's "New Regeneration" has been split into two; One obtained the Body (Human-Doctor) and one obtained the Doctor's Mind and thus the 11th reincarnation of the Doctor was born. Now, the theory behind this "11th incarnation" all derives from the fact that The Doctor did in fact start to regenerate regenerate at the end of The Stolen Earth, but actually transported the regeneration energy into his hand he lost in a battle with the Sycorax but because he was within the first 15 hours of his new incarnation he was able to grow it back. This only happened by the Doctor allowing his body to heal itself but then passing the Regneration energy to an object of the same genetic structure - His hand -thus enabling the Doctor to keep his current form.
― The Doctor
Now, because the Doctor managed to transfer the regeneration energy to this hand, the regeneration process still needs to be carried out. So, after the Doctor, Sarah Jane Smith, Rose Tyler, Jack Harkness and Martha Jones are captured, Donna was trapped inside the TARDIS. The hand then started to generate and formed an exact copy of the Doctor, but upon regenerating, Donna touched the hand causing the new incarnation to split into two - Mind and Body - The Doctor Donna (first heard be the Ood) and the Human Doctor; human because of the cross DNA between Donna and the hand upon regeneration. As the Hand was of Time Lord origin it already had all The Doctors thoughts and knowledge, therefore allowing for there to be 3 Doctors.
 The Human Doctor
The 'Metacrisis' Doctor
|Race:||Human-Time Lord Metacrisis|
|Home Planet:||Earth/Gallifrey (Currently lives in Pete's World|
|Debuts in:||Journey's End|
This half of the Biology Metacrisis was formed upon Donna touching the Doctor's hand upon it regenerating. With the hand packed full of regenerative energy it combined with the Human DNA of Donna Noble when she touched the hands casing. This force of this reaction caused the outer casing of the hand to shatter and allowing the missing body of the Doctor creating a new Time Lord/Human Hybrid. This body possess human qualities such as; Inability to regenerate, to age like Human and it only has one heart.
Because the newly grown Doctor was partially formed using Donna's DNA it had inherited Donna's mannerisms, but as able to keep the same memories, thoughts and feelings as the original Doctor all up to the point to which he forced the regeneration upon the severed hand. Up until that time, essentially, they were the same man but with Physical differences. But, as the original Doctor pointed out, this new 'clone' if the Doctor was born in war, it was full of anger, blood and revenge which is what was able to commit a mass genocide of an entire species and/or race (The Daleks); An act on which the Original Doctor had done in the Last Great Time War and has ever since condemned his actions. Because this version of the Doctor was born during a war he doesn't trust it to be let alone so he asks Rose to look after him when they arrive at Bad Wolf Bay in the parallel dimension; Pete's World. At first Rose didn't want to spend her life with the new Doctor was 'it wasn't him' but after the Doctor had explained to her that this Doctor has the same thought, feelings, emotions towards her and everything else he does she soon accepts it. The Doctor states that before he met Rose as his Ninth Incarnation he was the same, but Rose had helped him and made him better. Then Rose asks the Human-Doctor what was the last thing he said to her the last time they were standing on Bad Wolf Bay, the original Doctor says "Rose Tyler..." and the Human Doctor whispers the end of the sentence in her ear "I Love You" where Rose then kisses the Human Doctor. The Human Doctor proposes to then want to share the rest of his human life with Rose.
The Doctor looked on sadly as both Rose and the Human Doctor kissed, if not stoically, before looking back at Donna and going back into the TARDIS. As the TARDIS started to disappear, Rose broke the kiss and looked towards the TARDIS as the Human-Doctor held her hand to, what would look like, the last time they will ever see each other again.
 The Doctor Donna
|The Doctor Donna|
Doctor side awakening in Donna
|Race:||Human-Time Lord Metacrisis|
|Home Planet:||Earth (Possibly Gallifrey aswell)|
The Doctor Donna was formed when she touched the casing of The Doctor's Severed Hand and inadvertently mixing her DNA with the hand, allowing the energy from the regeneration flow into her. Allowing herself to so this she was able to become the Human-Doctor Metacris much like the Human Doctor, but commonly called Doctor Donna to avoid confusion, this 'Meta-crisis' allowed there to be a Human/Time Lord Hybrid. By becoming a Hybrid, Donna was able to become a Time Lord, but it lay dormant within her until her synapses got "That little extra spark" to jump start the Time Lord DNA. Within this DNA was also some of The Doctors mannerisms. Because of this she has the Doctors intelligence, and because of her human instinct, she can think and invent thing both Doctors could never think about. Because the Doctor Donna now has her Time Lord Intellect, she was able to disable the Reality Bomb with ease as well as stop the Daleks from using their weapons able to make them spin around uncontrollably to allow the others escape as well as this she and the Human Doctor sent all 27 planets back to their original locations and time zones. On her way back to Earth the Doctor Donna had trouble speaking and thinking, this is mainly because there cannot be a Human/Time Lord Hybid, if the Doctor didn't erase her memory she would have died. So the Doctor saved her life by wiping every memory of her time with the Doctor and in fact ever meeting him, and then taken home to her Mum and Grandad where they were instructed never to speak of him or any of the adventures they had or all the memories will come flooding back and she would "Burn Up".