In the mirror universe, Sestro was an Iyaaran in the 24th century.
In the 2340s, Sestro impersonated Jean-Luc Picard. While impersonating Picard, Sestro was captured by the rebels aboard the Lakul. Sestro was then imprisoned because the crew of the Lakul did not trust Picard. However, Sestro was able to escape and beamed down to the planet the Lakul was orbiting in order to save the Lakul's away team from a Klingon attack. In the rescue, Sestro was injured. Later, Sestro revealed that his people wished to undermine the Klingon-Cardassian Alliance, hence his deception. (STA - Mirror Universe- Shards and Shadows short story: "The Traitor")