1. Pre-Hartnell Doctor.
2. TARDIS got stuck in the shape of a Police Box, either deliberately, or malfunction.
3. Doctor returns to Gallifrey, has memory wiped, gets new regeneration cycle.
4. The TARDIS goes in for maintenance to repair chameleon circuit.
5. The Hartnell Doctor “borrows” a TARDIS, the same one the Doctor had before.
6. The TARDIS remembers the Doctor, reverts to Police Box form first chance it gets.
Only problem I can see with a pre-Hartnell Doctor is the number of incarnations. We supposedly have a full all-female cycle - 13 incarnations. Don’t additional cycles only add 12 regenerations - an additional 12 incarnations? Unless The Stolen Earth regeneration doesn’t count, Hartnell to Smith is 12 regenerations, with Hartnell effectively the 14th of 25 incarnations, which would make Smith either the last of the second cycle (25th) or the first of a third (26th).
2. TARDIS got stuck in the shape of a Police Box, either deliberately, or malfunction.
3. Doctor returns to Gallifrey, has memory wiped, gets new regeneration cycle.
4. The TARDIS goes in for maintenance to repair chameleon circuit.
5. The Hartnell Doctor “borrows” a TARDIS, the same one the Doctor had before.
6. The TARDIS remembers the Doctor, reverts to Police Box form first chance it gets.
Only problem I can see with a pre-Hartnell Doctor is the number of incarnations. We supposedly have a full all-female cycle - 13 incarnations. Don’t additional cycles only add 12 regenerations - an additional 12 incarnations? Unless The Stolen Earth regeneration doesn’t count, Hartnell to Smith is 12 regenerations, with Hartnell effectively the 14th of 25 incarnations, which would make Smith either the last of the second cycle (25th) or the first of a third (26th).