Timeless Child's realm

From Tardis Wiki, the free Doctor Who reference

In an account which the Spy Master claimed to have discovered in the Matrix, the Timeless Child, who would become the Time Lord known as the Doctor, hailed from a realm potentially within a separate dimension or universe from N-Space.

The child, the only known member of their species, was found on an unknown planet, near a monument beneath a wormhole (TV: The Timeless Children) to "another, unknown dimension". (PROSE: The Secrets of the Timeless Child) Later, Tecteun theorised that Universe Two might have been home to the Timeless Child's realm. The Thirteenth Doctor was less sure about this. (TV: Survivors of the Flux)

Ultimately, the child was found and taken to Gallifrey by the Shobogan Tecteun, where they became the template for the Time Lords. (TV: The Timeless Children)