Thad

Thad was a patient in the Welkin Sanatorium and Centre for Wellness. She was created by Sylvie to replace her previous child in her memory. As an android, she was unaffected by the virus on the planet which helped the Fifth Doctor and Tegan Jovanka realise their perception was off. She wanted to help the Doctor stop Luchino's plan and showed him to the hologram machine. After his mother's hologram was switched off, the Doctor took him, Fabrico and Aether Beauregarde to a save location. (AUDIO: The Lost Resort)