Paul Neville discovered Huvan's potential when he was fifteen. Neville genetically modified him so he remained physiologically an adolescent, making him more easily controllable.
When Huvan met the Fourth Doctor and Romana on Ashkellia, he was thirty-four. He became infatuated with Romana. Neville used him to access the higher dimensions through the Palace of the Old Ones, but lost control once he gained near infinite power.
However, once Huvan realised he could not make Romana love him, he became angry and threatened to destroy the universe. The Doctor and Romana convinced him not to do so, and gave him two other alternatives. One was to exile himself to another dimension as Valdemar had. The other was to erase his own memories and start life over as a new man.
Huvan chose the latter, transporting himself to another planet and turning himself into a trapper called Ponch. When he grew up, an older Romana returned and told him the story of what had happened on Ashkellia so he could remember who he had been. She regenerated into a younger woman and took him away in her TARDIS as her new companion. (PROSE: Tomb of Valdemar)