Complex sentence: This is finally explained, over 26 years later, during "The Christmas Invasion", when the Doctor explains that a Timelord has control over their physical form within the first 15 hours of a regeneration.
Split into simpler sentences: This is finally explained, over 26 years later, during "The Christmas Invasion". The Doctor explains that a Timelord has control over their physical form within the first 15 hours of a regeneration.