The Explosion

The Explosion was a type of regeneration in which a Time Lord was consumed by "a dramatic and instant burst" of fiery golden regeneration energy. Subtypes of the Explosion included the Slow Explosion and the Reverse Explosion. (PROSE: How to be a Time Lord)

By one accounts, the Doctor started regenerating in this manner due to the regeneration cycle granted by the Restoration. (PROSE: Doctor Who and the Time War)