The Secrets of the Timeless Child 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 Master in TV: The Timeless Children, albeit with a handful of minor differences.
"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 of 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 do the Shobogans become the Time Lords.
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- The Thirteenth Doctor's account as given in this story is generally congruent with the Master's in The Timeless Children, but differs in places. Most notably, the Master claimed that Tecteun had deliberately limited regeneration cycles to twelve "slots", whereas the Doctor's account has the Shobogans discover it as a strict, hardwired limit in the power itself.