The Secret of the Timeless Child (short story)

 was a short story included in Doctor Who The Official Annual 2021. Narrated by the Thirteenth Doctor, it retold the story of the Timeless Child, revealed by the Spy Master in TV: The Timeless Children, albeit with a handful of minor differences.

Summary
"Once upon several times", before the Time Lords took over the universe, an explorer named Tecteun becomes the first inhabitant of the obscure planet Gallifrey to venture into outer space. On a "distant, deserted world", she finds a gateway into another dimension.

After adopting the "abandoned" child, Tecteun travels some more and eventually returns to Gallifrey, where she studies the foundling in an effort to ascertain her origins. One day, in a "terrible accident", the child falls off a cliff and dies. However, she soon starts to glow and regenerates, becoming the first person on Gallifrey to do so.

Determined to crack the regeneration code, Tecteun becomes more and more obsessed with her research. After discovering the secret, she tests it on herself and then shares it with her fellow Shobogans, although they discover a "strict limit" to the power of regeneration: it can only be accomplished twelve times. Thus the Shobogans become the Time Lords.

Characters

 * Thirteenth Doctor
 * Timeless Child
 * Tecteun

Continuity

 * The Thirteenth Doctor goes over the history of the Timeless Child. (TV: The Timeless Children)