Fourth Timeless Child
According to the Spy Master, the Founding Fathers of Gallifrey built a lie about the existence of the Time Lords on the Timeless Child. It was buried deep in the memories and identity of all Time Lords. (TV: Spyfall)
When Remnants on the planet Desolation were taunting the Thirteenth Doctor about her fears, they looked "further back" into her past and referred to the Timeless Child.
We see what's hidden even from yourself, the outcast, abandoned and unknown.
When they made the reference, the Doctor was confused and asked them what they were talking about, then angrily told the Remnants to "get out of [her] head". (TV: The Ghost Monument)
When the Master learned the truth about the Timeless Child, he ravaged Gallifrey to "make them pay" for what he discovered. He told the Thirteenth Doctor that learning the truth had not been easy for him. When the Master first mentioned the Timeless Child mystery to the Doctor, she got a massive headache and a flashback to when the Remnants approached her, as well as a glimpse of a dark-skinned child wearing yellow robes and standing outside a tall building under a purple sky. (TV: Spyfall)
