Regeneration

Time Lords were known for their ability to change bodies, going through multiple lives.

In the 89067986779811167562948736197891674912223184th Universe, the Time Technicians Andro and Fabian had both regenerated before by the time they witnessed the First Doctor's theft of a certain faulty TARDIS, with one being on his second life, and the other on his eleventh. In addition, when he first encountered her, the Doctor briefly believed Jenny Nowhere to be a friend of his in a new body, perhaps Magnus, before she told him otherwise. (PROSE: How To Steal Timeships & To Influence Time Lords)