Донна Ноубл
In the series four finale of the revived series, "Journey's End", an injured Tenth Doctor manages to avert a full regeneration by channelling "excess regenerative energy" into his severed hand, allowing him to heal without changing form. The limb ends up developing into a half-human clone when Donna Noble touches it; the event, a "two-way" "Human-Time Lord Meta-Crisis", also gives Donna a Time Lord's mind.