I rewatched Twice Upon a Time the other day and noticed how sad Twelve's final moments are if you strip away the romance.

He releases the TARDIS hand break, and the engines groan and produce a distorted sound to what we're used to, it then takes off, and not long after the cloister bell sounds.

The TARDIS uses some kind of R2D2 language to communicate with the Doctor, coaxing him out of suicide and into regeneration to which he finally relents, all while the Cloister bell is still sounding.

Remove the beautiful music, and Twelve spends his final moments walking round his house, talking to himself, whilst ignoring his check engine light, which leads to the "Multiple Operation Failures" we see on the monitor as Thirteen takes her first breath.